Polynomial Equations

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SAT Math › Polynomial Equations

Questions 1 - 10
1

The graph of a polynomial crosses the $x$-axis at $x=-2$ and $x=3$, and just touches (bounces off) the $x$-axis at $x=1$. Which polynomial could represent this behavior with the least possible degree and leading coefficient $1$?

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

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

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

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

Explanation

We need a polynomial that crosses the $x$-axis at $x=-2$ and $x=3$, and touches (bounces off) at $x=1$. When a polynomial crosses the $x$-axis at a point, the corresponding factor has odd multiplicity (usually 1); when it touches without crossing, the factor has even multiplicity (usually 2). Therefore, we need factors $(x+2)^1$, $(x-3)^1$, and $(x-1)^2$. The polynomial with least degree and leading coefficient 1 is $(x+2)(x-3)(x-1)^2$. This gives the correct crossing/touching behavior at each intercept. Remember: odd multiplicity means crossing, even multiplicity means touching.

2

On the coordinate plane, a polynomial curve touches the $x$-axis at $x=-2$ (does not cross) and crosses the $x$-axis at $x=1$. Which polynomial matches this intercept behavior with the least possible degree and a positive leading coefficient?

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

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

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

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

Explanation

We need a polynomial that touches (doesn't cross) at $x=-2$ and crosses at $x=1$. Touching without crossing indicates even multiplicity, while crossing indicates odd multiplicity. At $x=-2$, we need factor $(x+2)^2$ (even multiplicity); at $x=1$, we need factor $(x-1)^1$ (odd multiplicity). The polynomial with least degree and positive leading coefficient is $(x+2)^2(x-1)$. This has degree 3 and expands with positive leading coefficient. The key insight is that the graph's behavior at each intercept determines the required multiplicity of the corresponding factor.

3

The polynomial $r(x)=x^2+6x+9$ is used to find a repeated root. Which statement correctly identifies the zero(s) of $r(x)$ and how the graph meets the x-axis there?

Zeros at $x=-9,0$; crosses

Zero at $x=3$; crosses

Zero at $x=-3$; touches

Zero at $x=9$; touches

Explanation

We need to find the zeros of $r(x)=x^2+6x+9$ and determine how the graph meets the x-axis. First, we can factor this quadratic: we need two numbers that multiply to 9 and add to 6, which are both 3. So $r(x) = (x+3)(x+3) = (x+3)^2$. Setting this equal to zero: $(x+3)^2 = 0$ gives $x = -3$ with multiplicity 2. Since the zero has even multiplicity, the graph touches but doesn't cross the x-axis at $x=-3$. This is a perfect square trinomial, which always results in a repeated root where the parabola just touches the x-axis.

4

If $$q(x)=(x-7)(x^2+7x+49),$$ what is $q(x)$ in standard form? This uses the difference of cubes pattern, so

$x^3-49x-343$

$x^3+343$

$x^3+49x-343$

$x^3-343$

Explanation

We need to expand $q(x)=(x-7)(x^2+7x+49)$, which follows the difference of cubes pattern. Distributing: $x(x^2+7x+49) - 7(x^2+7x+49) = x^3 + 7x^2 + 49x - 7x^2 - 49x - 343$. Combining like terms: $x^3 + (7-7)x^2 + (49-49)x - 343 = x^3 - 343$. This is indeed $x^3 - 7^3$, confirming the difference of cubes pattern: $(a-b)(a^2+ab+b^2) = a^3-b^3$. The middle terms cancel out, which is characteristic of this special factorization. Recognizing special patterns like difference of cubes can save time and reduce errors.

5

A polynomial $p(x)$ is in standard form as $$p(x)=x^6-3x^2+10.$$ What is the degree of $p(x)$, and what does that imply about the maximum number of x-intercepts its graph can have?

2

4

6

8

Explanation

The polynomial $p(x)=x^6-3x^2+10$ is already in standard form, and we need to identify its degree. The degree is the highest power of x with a non-zero coefficient, which is 6 (from the $x^6$ term). A polynomial of degree 6 can have at most 6 real zeros, which means its graph can have at most 6 x-intercepts. Note that this polynomial has no odd-degree terms ($x^5$, $x^3$, $x$), making it an even function. Don't be misled by the missing terms; the degree is still determined by the highest power present.

6

A polynomial is $m(x)=2x^4-8x^3+6x^2$. What is the greatest common factor (GCF) factored form of $m(x)$, keeping the remaining factor as a polynomial?

$2x(x^3-4x^2+3x)$

$2x^2(x^2-8x+6)$

$2x^2(x^2-4x+3)$

$x^2(2x^2-8x+6)$

Explanation

To factor $m(x)=2x^4-8x^3+6x^2$, we first identify the greatest common factor (GCF) of all terms. Each term has a factor of $x^2$: $2x^4 = 2x^2 \cdot x^2$, $-8x^3 = -8x^2 \cdot x$, $6x^2 = 6x^2 \cdot 1$. The coefficients 2, -8, and 6 have GCF of 2. Therefore, the overall GCF is $2x^2$. Factoring this out: $m(x) = 2x^2(x^2 - 4x + 3)$. We can verify by expanding: $2x^2(x^2 - 4x + 3) = 2x^4 - 8x^3 + 6x^2$ ✓. Always factor out the GCF first when working with polynomials, as it simplifies further factoring steps.

7

Compute the product $$(x^2+2x-3)(x-4)$$. Which option gives the correct expanded polynomial in standard form, after distributing and combining like terms?

$x^3+2x^2-11x-12$

$x^3-2x^2-11x+12$

$x^3+2x^2-5x-12$

$x^3-2x^2-5x+12$

Explanation

We need to expand $ (x^2+2x-3)(x-4) $ by distributing each term in the first polynomial to $ (x-4) $. First, distribute $x^2$: $x^2(x) - x^2(4) = x^3 - 4x^2$. Next, distribute $2x$: $2x(x) - 2x(4) = 2x^2 - 8x$. Finally, distribute $-3$: $-3(x) - (-3)(4) = -3x + 12$. Combining all terms: $x^3 - 4x^2 + 2x^2 - 8x - 3x + 12 = x^3 - 2x^2 - 11x + 12$. The key is to carefully track signs, especially when distributing negative terms. When multiplying polynomials, organize your work to avoid missing terms or making sign errors.

8

A polynomial $k(x)$ has degree $4$ and real zeros at $x=-1$ and $x=2$ (with $x=2$ having multiplicity $3$). Which expression could be $k(x)$ if the leading coefficient is $5$?

$5(x-1)(x+2)^3$

$5(x+1)^3(x-2)$

$5(x+1)(x-2)^3$

$-5(x+1)(x-2)^3$

Explanation

The polynomial has degree 4 with zeros at $x=-1$ (multiplicity 1) and $x=2$ (multiplicity 3), and leading coefficient 5. Since the multiplicities must sum to the degree: 1 + 3 = 4 ✓. The factored form is $k(x) = 5(x-(-1))^1(x-2)^3 = 5(x+1)(x-2)^3$. The factor $(x+1)$ corresponds to the zero at $x=-1$, and $(x-2)^3$ corresponds to the zero at $x=2$ with multiplicity 3. The graph will cross at $x=-1$ (odd multiplicity) and have a flattened crossing at $x=2$ (odd multiplicity ≥ 3). When constructing polynomials from zeros and multiplicities, ensure the sum of multiplicities equals the degree.

9

On a coordinate plane, the graph of a polynomial crosses the x-axis at $x=-3$ and just touches (bounces off) the x-axis at $x=1$. Which factored form matches this intercept information and has a positive leading coefficient?

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

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

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

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

Explanation

The graph crosses the x-axis at $x=-3$ (indicating odd multiplicity) and touches/bounces at $x=1$ (indicating even multiplicity). With a positive leading coefficient, the simplest polynomial matching this behavior is $(x+3)(x-1)^2$. The factor $(x+3)$ has multiplicity 1 (odd), so the graph crosses at $x=-3$. The factor $(x-1)^2$ has multiplicity 2 (even), so the graph touches but doesn't cross at $x=1$. The positive leading coefficient (which is 1 when expanded) ensures the polynomial goes to $+infty$ as $x o infty$. Remember that crossing behavior at x-intercepts is determined by the multiplicity: odd multiplicities cross, even multiplicities touch.

10

A polynomial is defined by $$f(x)=x^3-6x^2+11x-6.$$ Which value is a zero of $f(x)$, meaning it is an x-intercept of the graph of $y=f(x)$?

$6$

$4$

$1$

$-1$

Explanation

To find which value is a zero of $f(x)=x^3-6x^2+11x-6$, we need to test each option by substitution. Testing $x=1$: $f(1) = 1^3 - 6(1)^2 + 11(1) - 6 = 1 - 6 + 11 - 6 = 0$. Since $f(1) = 0$, we know $x=1$ is a zero. We can verify by factoring: since $(x-1)$ is a factor, we can use polynomial division to find $f(x) = (x-1)(x^2-5x+6) = (x-1)(x-2)(x-3)$. The zeros are $1$, $2$, and $3$. For polynomial zero problems, the rational root theorem can help narrow down candidates to test.

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