Use Factoring, Squares to Analyze Graphs
Help Questions
Algebra › Use Factoring, Squares to Analyze Graphs
Complete the square to rewrite $f(x)=x^2-6x+11$ in vertex form, then identify the vertex and axis of symmetry.
Vertex: $(3,2)$; axis of symmetry: $x=3$
Vertex: $(3,11)$; axis of symmetry: $x=3$
Vertex: $(-3,2)$; axis of symmetry: $x=-3$
Vertex: $(6,11)$; axis of symmetry: $x=6$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. To complete the square for f(x) = x² - 6x + 11: half of -6 is -3, squared is 9. Adding and subtracting: f(x) = (x² - 6x + 9) - 9 + 11 = (x - 3)² + 2. The vertex form shows vertex at (3, 2), and the axis of symmetry is the vertical line x = 3. Choice A correctly completes the square to get (x - 3)² + 2 showing vertex at (3, 2) and axis at x = 3. Choice C finds the axis of symmetry correctly but places the vertex at the wrong coordinates: the axis is x = 3, and substituting into the original function gives y = 9 - 18 + 11 = 2, so vertex is (3, 2), not (3, 11). The axis gives you the x-coordinate, but you still need to find the y-coordinate! The three forms, three features connection: Standard form (ax² + bx + c) → see y-intercept c immediately. Factored form (a(x-p)(x-q)) → see zeros p, q immediately. Vertex form (a(x-h)²+k) → see vertex (h,k) immediately. Each form is optimized to show certain features! Convert to the form that shows what you need.
Complete the square for $r(x)=2x^2+12x+10$ to find the vertex and the minimum value.
Vertex $(-6,10)$; minimum value $10$
Vertex $(-3,-8)$; minimum value $-8$
Vertex $(3,-8)$; minimum value $-8$
Vertex $(-3,8)$; minimum value $8$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. To complete the square for r(x) = 2x² + 12x + 10: first factor out the 2 from the first two terms: r(x) = 2(x² + 6x) + 10. Half of 6 is 3, squared is 9. So r(x) = 2(x² + 6x + 9) - 2(9) + 10 = 2(x + 3)² - 18 + 10 = 2(x + 3)² - 8. The vertex form shows vertex at (-3, -8), which is the minimum since a = 2 > 0. The minimum value is -8. Choice A correctly completes the square to get 2(x + 3)² - 8 showing vertex at (-3, -8) and minimum value -8. Choice B has a sign error: from (x + 3)², the h-value is -3 (not 3). Remember in vertex form a(x - h)² + k, if you have (x + 3) = (x - (-3)), then h = -3. The sign in the parentheses is opposite to the x-coordinate of the vertex! Completing the square reminder: for x² + 6x, the perfect square you add is (6/2)² = 3² = 9. When there's a coefficient a in front, factor it out first, complete the square inside, then multiply back through. Watch signs carefully when finding b/2!
Which form of the function best shows the vertex of $f(x)=x^2+4x-12$ and what is that vertex? (Use completing the square.)
Vertex form: $f(x)=(x+2)^2-16$; vertex: $(-2,-16)$
Vertex form: $f(x)=(x-2)^2-16$; vertex: $(2,-16)$
Vertex form: $f(x)=(x+2)^2-12$; vertex: $(-2,-12)$
Vertex form: $f(x)=(x+4)^2-16$; vertex: $(-4,-16)$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. To complete the square for f(x) = x² +4x -12: half of 4 is 2, squared is 4. Adding and subtracting: f(x) = (x² +4x +4) -4 -12 = (x +2)² -16. The vertex form shows vertex at (-2, -16). Choice A correctly completes the square to get (x+2)² -16 showing vertex at (-2, -16). Choice B makes an error completing the square: it uses (x-2) instead of (x+2), flipping the sign of h to 2—half of 4 is 2, but since b=4>0, it's (x+2), watch the sign! Completing the square reminder: for x² + [b]x, the perfect square you add is (b/2)²—half the middle coefficient, then square it. If you have x² + 8x, that's (8/2)² = 4² = 16. If you have x² - 6x, that's (-6/2)² = (-3)² = 9. Watch signs carefully when finding b/2! The three forms, three features connection: Standard form (ax² + bx + c) → see y-intercept c immediately. Factored form (a(x-p)(x-q)) → see zeros p, q immediately. Vertex form (a(x-h)²+k) → see vertex (h,k) immediately. Each form is optimized to show certain features! Convert to the form that shows what you need.
Use factoring to analyze $h(x)=2x^2-10x+12$. Identify the zeros (x-intercepts) and the axis of symmetry.
Zeros: $x=1, x=6$; axis of symmetry: $x=\tfrac{7}{2}$
Zeros: $x=-2, x=-3$; axis of symmetry: $x=-\tfrac{5}{2}$
Zeros: $x=2, x=3$; axis of symmetry: $x=\tfrac{5}{2}$
Zeros: $x=2, x=3$; axis of symmetry: $x=5$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Factoring a quadratic into the form f(x) = a(x - p)(x - q) immediately reveals the zeros (x-intercepts) at x = p and x = q: these are where the parabola crosses the x-axis. From the zeros, you can also find the axis of symmetry—it's the vertical line exactly halfway between the zeros at x = (p + q)/2, and the vertex sits on this axis! To find the zeros of h(x) = 2x² -10x +12, first factor out the 2: 2(x² -5x +6), then factor: looking for numbers that multiply to 6 and add to -5, we find -2 and -3. So h(x) = 2(x -2)(x -3). Setting each factor to zero: x -2 =0 gives x=2, x-3=0 gives x=3. These are our zeros! The axis of symmetry is at x = (2 + 3)/2 = 5/2, exactly halfway between the zeros. Choice A correctly factors to get 2(x-2)(x-3) showing zeros at x=2,3 and axis at x=5/2. Choice C has the zeros right but calculates the axis of symmetry incorrectly: with zeros at x=2 and x=3, the axis is at the midpoint x=(2+3)/2=5/2, not 5—maybe doubling instead of averaging. The axis is always exactly halfway between the two zeros! Feature-finding strategy: (1) Need zeros? Factor into (x - p)(x - q) form and set factors = 0. (2) Need vertex? Complete the square to get (x - h)² + k form and read (h, k). (3) Need axis of symmetry? Use x = h from vertex OR x = (p + q)/2 from zeros OR x = -b/(2a) from standard form—all three work! (4) Need extreme value? It's k from vertex form. Choose the right tool for what you need! The sign trick for factored form: if you have (x - 3), the zero is x = 3 (opposite sign); if you have (x + 5) = (x - (-5)), the zero is x = -5 (opposite sign). The zero always has the opposite sign from what appears in the factor. This trips everyone up at first—practice makes it automatic!
Factor $q(x)=x^2+2x-15$ to find the zeros and the axis of symmetry.
Zeros: $x=-3, x=-5$; Axis of symmetry: $x=-4$
Zeros: $x=-3, x=5$; Axis of symmetry: $x=1$
Zeros: $x=3, x=-5$; Axis of symmetry: $x=-1$
Zeros: $x=3, x=5$; Axis of symmetry: $x=4$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Factoring a quadratic into the form f(x) = a(x - p)(x - q) immediately reveals the zeros (x-intercepts) at x = p and x = q: these are where the parabola crosses the x-axis. From the zeros, you can also find the axis of symmetry—it's the vertical line exactly halfway between the zeros at x = (p + q)/2, and the vertex sits on this axis! To find the zeros of q(x) = x² + 2x - 15, we factor: looking for two numbers that multiply to -15 and add to 2, we find 5 and -3. So q(x) = (x + 5)(x - 3). Setting each factor to zero: x + 5 = 0 gives x = -5, and x - 3 = 0 gives x = 3. These are our zeros! The axis of symmetry is at x = (3 + (-5))/2 = -2/2 = -1, exactly halfway between the zeros. Choice A correctly factors to get (x - 3)(x + 5) showing zeros at x = 3, -5 and axis at x = -1. Choice B has the zeros reversed: from (x + 5)(x - 3), the zeros are x = -5 and x = 3 (not x = -3 and x = 5). Remember: (x + 5) = 0 gives x = -5, and (x - 3) = 0 gives x = 3. The sign in the factor determines the sign of the zero! The sign trick for factored form: if you have (x - 3), the zero is x = 3 (same sign); if you have (x + 5) = (x - (-5)), the zero is x = -5 (opposite sign from what appears). The zero always matches what comes after the minus sign in (x - p) form. This trips everyone up at first—practice makes it automatic!
A ball’s height (in feet) after $t$ seconds is $h(t)=-t^2+10t+4$. Use completing the square to find the maximum height and when it occurs.
Maximum height $25$ at $t=5$
Minimum height $29$ at $t=5$
Maximum height $29$ at $t=5$
Maximum height $29$ at $t=-5$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. In this context where h(t) models the ball's height over time, completing the square reveals the maximum height of 29 feet occurs at t = 5 seconds. The vertex form tells us the extreme value—crucial for understanding the real-world situation! To complete the square: h(t) = -(t² - 10t) + 4 = - (t² - 10t + 25 - 25) + 4 = - ((t - 5)² - 25) + 4 = - (t - 5)² + 25 + 4 = - (t - 5)² + 29. Choice A correctly completes the square to get - (t - 5)² + 29 showing maximum height 29 at t=5. Choice B makes an error completing the square: it calculates (b/2)² as 25 but forgets to add back the +4 properly, getting 25 instead of 29—after -(-25) it's +25 +4=29! For applied problems: zeros often mean 'when does quantity reach zero' (ball hits ground, profit = 0, etc.), and vertex often means 'what's the best/worst outcome' (maximum height, minimum cost, etc.). Translate the math features (zeros, vertex) into context language (when, how much, what's optimal) to fully answer the question!
Which form of a quadratic function best shows the vertex immediately?
Any form shows the vertex immediately without rewriting
Factored form: $f(x)=a(x-p)(x-q)$
Standard form: $f(x)=ax^2+bx+c$
Vertex form: $f(x)=a(x-h)^2+k$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. The three forms of a quadratic each reveal different features: standard form f(x) = ax² + bx + c shows the y-intercept (c) clearly; factored form f(x) = a(x - p)(x - q) shows the zeros (p and q); vertex form f(x) = a(x - h)² + k shows the vertex (h, k) and extreme value (k). Knowing how to convert between forms lets you see whichever features you need! Vertex form f(x) = a(x - h)² + k is specifically designed to show the vertex at (h, k) immediately—you can literally read it off without any calculation. In contrast, standard form requires completing the square or using x = -b/(2a), and factored form requires finding the midpoint of zeros. Choice C correctly identifies vertex form f(x) = a(x - h)² + k as the form that shows the vertex immediately. Choice D is incorrect: you cannot see the vertex immediately from standard or factored form without doing some work. Standard form requires the formula x = -b/(2a) for the axis, then substitution for the y-coordinate. Factored form requires finding zeros first, then their midpoint. The three forms, three features connection: Each form is optimized to show certain features! Vertex form → see vertex (h, k) immediately. Factored form → see zeros immediately. Standard form → see y-intercept immediately. Choose the form that matches what you need to find!
Complete the square for $g(x)=x^2+8x+7$ to find the vertex and the minimum value.
Vertex: $(-8,7)$; minimum value: $7$
Vertex: $(-4,-9)$; maximum value: $-9$
Vertex: $(-4,-9)$; minimum value: $-9$
Vertex: $(4,9)$; minimum value: $9$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. To complete the square for g(x) = x² + 8x + 7: half of 8 is 4, squared is 16. Adding and subtracting: g(x) = (x² + 8x + 16) - 16 + 7 = (x + 4)² - 9. The vertex form shows vertex at (-4, -9), which is the minimum since a = 1 > 0. The minimum value is -9. Choice B correctly completes the square to get (x + 4)² - 9 showing vertex at (-4, -9) and minimum value -9. Choice C identifies the vertex correctly but confuses maximum with minimum: since a = 1 is positive, the parabola opens up, making the vertex a minimum, not a maximum. The sign of a determines whether the vertex is the highest or lowest point! Completing the square reminder: for x² + 8x, the perfect square you add is (8/2)² = 4² = 16—half the middle coefficient, then square it. If you have x² + 8x, that's (8/2)² = 4² = 16. If you have x² - 6x, that's (-6/2)² = (-3)² = 9. Watch signs carefully when finding b/2!
Use factoring to analyze $f(x)=x^2-9$: find the zeros and the axis of symmetry.
Zeros: $x=0, x=9$; Axis of symmetry: $x=\frac{9}{2}$
Zeros: $x=3, x=-3$; Axis of symmetry: $x=0$
Zeros: $x=3, x=-3$; Axis of symmetry: $x=3$
Zeros: $x=-9, x=1$; Axis of symmetry: $x=-4$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Factoring a quadratic into the form f(x) = a(x - p)(x - q) immediately reveals the zeros (x-intercepts) at x = p and x = q: these are where the parabola crosses the x-axis. From the zeros, you can also find the axis of symmetry—it's the vertical line exactly halfway between the zeros at x = (p + q)/2, and the vertex sits on this axis! To find the zeros of f(x) = x² - 9, we recognize this as a difference of squares: f(x) = x² - 3² = (x + 3)(x - 3). Setting each factor to zero: x + 3 = 0 gives x = -3, and x - 3 = 0 gives x = 3. These are our zeros! The axis of symmetry is at x = (-3 + 3)/2 = 0/2 = 0, exactly halfway between the zeros. Choice B correctly factors to get (x + 3)(x - 3) showing zeros at x = 3, -3 and axis at x = 0. Choice C has the zeros right but calculates the axis of symmetry incorrectly: with zeros at x = -3 and x = 3, the axis is at the midpoint x = (-3 + 3)/2 = 0, not 3. The axis is always exactly halfway between the two zeros! The three forms, three features connection: Standard form (ax² + bx + c) → see y-intercept c immediately. Factored form (a(x-p)(x-q)) → see zeros p, q immediately. Vertex form (a(x-h)²+k) → see vertex (h,k) immediately. Each form is optimized to show certain features! Convert to the form that shows what you need.
Use completing the square to analyze $u(x)=x^2+10x+9$. Which statement gives the correct vertex and axis of symmetry?
Vertex: $(-10,9)$; axis of symmetry: $x=-10$
Vertex: $(-5,-16)$; axis of symmetry: $x=-5$
Vertex: $(5,34)$; axis of symmetry: $x=5$
Vertex: $(-5,16)$; axis of symmetry: $x=-5$
Explanation
This question tests your ability to use factoring and completing the square—two powerful techniques—to reveal important features of quadratic graphs like zeros (x-intercepts), vertex (the maximum or minimum point), and the axis of symmetry. Completing the square transforms a quadratic into vertex form f(x) = a(x - h)² + k, which reveals the vertex at (h, k) instantly—no calculation needed once you're in this form! The k-value is the maximum (if a < 0, opens down) or minimum (if a > 0, opens up), and the axis of symmetry is the vertical line x = h through the vertex. To complete the square for u(x) = x² + 10x + 9: half of 10 is 5, squared is 25. Adding and subtracting: u(x) = (x² + 10x + 25) - 25 + 9 = (x + 5)² - 16. The vertex form shows vertex at (-5, -16), and the axis of symmetry is the vertical line x = -5. Choice B correctly completes the square to get (x + 5)² - 16 showing vertex at (-5, -16) and axis at x = -5. Choice D makes an error completing the square: it calculates -25 + 9 as 16 instead of -16. When you add and subtract to complete the square, be careful with the arithmetic: -25 + 9 = -16, not 16! Completing the square reminder: for x² + 10x, the perfect square you add is (10/2)² = 5² = 25—half the middle coefficient, then square it. Then carefully compute the constant term: original constant (9) minus what you added (25) gives 9 - 25 = -16. Watch signs carefully!