Polynomial Equations

Help Questions

PSAT Math › Polynomial Equations

Questions 1 - 10
1

A polynomial is given by $f(x)=x^3-6x^2+11x-6$. Which set lists all zeros of $f(x)$? Be careful not to confuse factors with roots or miss a repeated factor.

${1,2,6}$

${-1,2,3}$

${1,2,3}$

${0,2,3}$

Explanation

To find the zeros of $f(x)=x^3-6x^2+11x-6$, we need to solve $f(x)=0$. Testing small integer values, we find $f(1)=1-6+11-6=0$, so $(x-1)$ is a factor. Using polynomial division or synthetic division, we get $f(x)=(x-1)(x^2-5x+6)$. Factoring the quadratic: $(x-1)(x-2)(x-3)$, giving zeros at $x=1, 2, 3$. Students often confuse the factors $(x-a)$ with the roots $x=a$, or miss testing $x=1$ as a potential zero. Always verify your zeros by substituting back into the original polynomial.

2

What is the product of the polynomials $(2x-5)(x^2+3x-4)$, written in standard form? Watch for sign errors when combining like terms after distributing.

$2x^3+x^2-23x-20$

$2x^3+x^2-23x+20$

$2x^3+x^2-22x+20$

$2x^3-x^2-23x+20$

Explanation

To find the product $(2x-5)(x^2+3x-4)$, we distribute each term in the first polynomial to every term in the second. This gives us $2x(x^2+3x-4) - 5(x^2+3x-4) = 2x^3+6x^2-8x-5x^2-15x+20$. Combining like terms: $2x^3+(6x^2-5x^2)+(-8x-15x)+20 = 2x^3+x^2-23x+20$. The most common error is sign mistakes when distributing the $-5$, forgetting that $-5 imes -4 = +20$. Always double-check signs when distributing negative terms.

3

A student simplifies the expression $(x-4)(x+3)+2(x-4)$. Which expression is equivalent to the original and written in factored form? Be careful not to distribute incorrectly or forget a common factor.

$x^2+x-4$

$(x-4)(x+5)$

$(x-4)(x+1)$

$(x+3)(x+2)$

Explanation

We need to factor the expression $(x-4)(x+3)+2(x-4)$. Notice that $(x-4)$ appears in both terms, making it a common factor. Factoring out $(x-4)$ gives us $(x-4)[(x+3)+2] = (x-4)(x+5)$. A common error is to distribute first instead of recognizing the common factor, which makes the problem unnecessarily complex. When you see repeated factors, always look to factor first before expanding.

4

Consider the polynomial $p(x)=(x^2-9)(x^3+2x)$. What is the degree of $p(x)$? Some students incorrectly add degrees within a factor instead of using the highest power in each factor.

3

4

5

6

Explanation

To find the degree of $p(x)=(x^2-9)(x^3+2x)$, we need the highest power of $x$ when expanded. The highest power comes from multiplying the highest powers in each factor: $x^2 cdot x^3 = x^5$. Therefore, the degree is 5. A common mistake is adding the degrees within each factor (like thinking $x^3+2x$ has degree 4) instead of identifying the highest power term. Remember: degree is determined by the single highest power, not the sum of powers.

5

Which expression is the polynomial $x^2-7x-18$ written in factored form? A common mistake is choosing factors that multiply to $-18$ but add to $-7$ incorrectly.

$(x-9)(x+2)$

$(x-6)(x-3)$

$(x+9)(x-2)$

$(x+6)(x-3)$

Explanation

To factor $x^2-7x-18$, we need two numbers that multiply to $-18$ and add to $-7$. Testing factor pairs of $-18$: $(-9)(2) = -18$ and $-9 + 2 = -7$, which works! So $x^2-7x-18 = (x-9)(x+2)$. A common error is finding factors that multiply correctly but forgetting to check if they add to the middle coefficient. When the constant term is negative, one factor must be positive and one negative.

6

A polynomial is defined by $k(x)=(x-1)^2(x+4)$. How many distinct real zeros does $k(x)$ have? A common wrong path is counting multiplicity as separate distinct zeros.

1

2

3

4

Explanation

The polynomial $k(x)=(x-1)^2(x+4)$ has zeros where each factor equals zero. Setting $(x-1)^2=0$ gives $x=1$ (with multiplicity 2), and $(x+4)=0$ gives $x=-4$. Though $x=1$ appears with multiplicity 2, it's still just one distinct zero. Therefore, $k(x)$ has exactly 2 distinct real zeros: $x=1$ and $x=-4$. Don't confuse multiplicity with the number of distinct zeros—a repeated root counts as one distinct zero.

7

A polynomial is given in factored form as $f(x)=(x+2)(x-5)(x^2+1)$. Which set lists all real zeros of $f(x)$? Some answers incorrectly include complex roots from $x^2+1=0$ as real zeros.

${2,-5}$

${-2,5,1}$

${-2,5}$

${-2,5,i,-i}$

Explanation

This question asks for all real zeros of $f(x)=(x+2)(x-5)(x^2+1)$. A polynomial equals zero when any of its factors equals zero. Setting each factor to zero: $x+2=0$ gives $x=-2$, $x-5=0$ gives $x=5$, and $x^2+1=0$ gives $x^2=-1$, which has no real solutions (only complex solutions $x=±i$). Therefore, the real zeros are only $x=-2$ and $x=5$. The key error to avoid is including complex roots like $i$ and $-i$ when asked specifically for real zeros. Remember that $x^2+1$ has no real zeros because squares of real numbers are never negative.

8

The polynomial $g(x)=x^3-6x^2+11x-6$ has zeros at $x=1,2,3$. Which expression is $g(x)$ written in completely factored form? A plausible wrong path is to miss a sign and use $(x+1)$ instead of $(x-1)$.

$(x+1)(x-2)(x-3)$

$(x-1)(x^2-5x+6)$

$(x-1)(x-2)(x+3)$

$(x-1)(x-2)(x-3)$

Explanation

We're given that $g(x)=x^3-6x^2+11x-6$ has zeros at $x=1,2,3$, and we need to write it in factored form. If a polynomial has zeros at these values, then $(x-1)$, $(x-2)$, and $(x-3)$ are factors. Therefore, $g(x)=(x-1)(x-2)(x-3)$. We can verify by expanding: $(x-1)(x-2)=x^2-3x+2$, then $(x^2-3x+2)(x-3)=x^3-3x^2-3x^2+9x+2x-6=x^3-6x^2+11x-6$. A common sign error is writing $(x+1)$ instead of $(x-1)$ for a zero at $x=1$. Remember: if $a$ is a zero, then $(x-a)$ is the corresponding factor.

9

A polynomial is shown on the coordinate plane. It has end behavior rising to the left and falling to the right, and it crosses the $x$-axis at $x=-1$, $x=2$, and $x=4$. Which could be a possible factored form of the polynomial?

$-(x+1)(x-2)(x-4)$

$(x+1)(x-2)(x-4)$

$(x+1)(x-2)^2(x-4)$

$-(x-1)(x-2)(x-4)$

Explanation

The question asks for a possible factored form of a polynomial that rises to the left, falls to the right, and crosses the x-axis at x=-1, 2, 4. This end behavior indicates an odd degree with negative leading coefficient. With three distinct crossings, the least-degree form is degree 3 with multiplicity 1 at each root: -(x+1)(x-2)(x-4), yielding a -x³ leading term matching the behavior. The factored form connects the roots and leading sign to the graph's intercepts and ends. Common errors include choosing a positive leading coefficient or incorrect roots, like x=1 in choice C. A test-taking strategy is to determine the leading coefficient's sign from end behavior and ensure factors align with given roots.

10

A quadratic models the height of a ball: $h(t)=-t^2+6t+7$. Which expression gives $h(t)$ in factored form, making the zeros (when the ball hits the ground) easiest to identify?

$-(t-7)(t+1)$

$-(t+7)(t-1)$

$(t-7)(t+1)$

$-(t-1)(t-7)$

Explanation

The question seeks the factored form of h(t) = -t² + 6t + 7 that makes the zeros easiest to identify. Factor out the negative: h(t) = -(t² - 6t - 7). The quadratic t² - 6t - 7 factors to (t-7)(t+1), as the factors of -7 summing to -6 are 1 and -7. Thus, h(t) = -(t-7)(t+1), revealing zeros at t=7 and t=-1 directly from the factors. This factored form emphasizes how roots correspond to when each linear factor is zero. A key error is selecting incorrect factor pairs or mishandling the negative sign. A test-taking strategy is to expand the choices back to standard form to verify the match.

Page 1 of 3