Applying the Remainder Theorem
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Algebra 2 › Applying the Remainder Theorem
If the remainder when $p(x)=x^4+mx^2-2x+1$ is divided by $(x-2)$ is $9$, what is $m$? (Use: remainder $=p(2)$.)
$m=1$
$m=0$
$m=2$
$m=-1$
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! The Remainder Theorem states that when you divide a polynomial p(x) by (x - a), the remainder is simply p(a)—just substitute a into the polynomial and evaluate! This works because of how polynomial division works: p(x) = (x - a)·q(x) + r, where r is the remainder. Substituting x = a: p(a) = (a - a)·q(a) + r = 0 + r = r. So the remainder r equals p(a)—brilliant! For (x-2), a=2, $p(2)=2^4$ $+m2^2$ -22 +1=16+4m-4+1=13+4m; set to 9: 13+4m=9, 4m=-4, m=-1. Choice A correctly finds m=-1. A distractor like C (1) might come from setting 16+4m-4+1=9 as 13+4m=9 but solving 4m=-4 incorrectly. Using the Remainder Theorem: (1) Identify the divisor (x - a) and extract a (remember: (x + 3) = (x - (-3)), so a = -3), (2) Substitute a for every x in p(x), (3) Calculate carefully (use parentheses for negative values!), (4) That result is your remainder. If it equals 0, (x - a) is a factor! This method is dramatically faster than polynomial long division.
Is $(x+2)$ a factor of $p(x)=x^3+3x^2-4x-12$? Use the Remainder Theorem / Factor Theorem (i.e., $(x-a)$ is a factor iff $p(a)=0$).
Yes, because $p(2)=0$.
No, because the remainder is $0$.
Yes, because $p(-2)=0$.
No, because $p(-2)=8$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! A special case is the Factor Theorem: (x - a) is a factor of p(x) if and only if p(a) = 0. This means the remainder is zero, so the division is exact with no remainder. We can test potential factors by just evaluating the polynomial—if p(a) = 0, we've found a factor! This beats trial-and-error factoring when testing specific values. For (x + 2) = (x - (-2)), a = -2; p(-2) = $(-2)^3$ + $3*(-2)^2$ - 4*(-2) - 12 = -8 + 3*4 + 8 - 12 = -8 + 12 + 8 - 12, which is (-8 - 12) + (12 + 8) = -20 + 20 = 0. Choice A correctly determines that yes, it is a factor because p(-2) = 0. Choice B says no because p(-2) = 8, which might come from forgetting to include the -12 or mishandling signs, but actually it's 0—keep track of all terms! Sign safety for negatives: when testing (x + 2) = (x - (-2)), you're evaluating at a = -2. Substitute carefully: if p(x) = x³ - 3x + 5, then p(-2) = (-2)³ - 3(-2) + 5 = -8 + 6 + 5 = 3. Use parentheses around negative values to avoid sign errors! This is where most mistakes happen with the Remainder Theorem.
Use the Remainder Theorem to find the remainder when $p(x)=3x^3-x^2-7x+2$ is divided by $(x+2)$.
The remainder is $12$.
The remainder is $-12$.
The remainder is $0$.
The remainder is $-6$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! The Remainder Theorem states that when you divide a polynomial p(x) by (x - a), the remainder is simply p(a)—just substitute a into the polynomial and evaluate! This works because of how polynomial division works: p(x) = (x - a)·q(x) + r, where r is the remainder. Substituting x = a: p(a) = (a - a)·q(a) + r = 0 + r = r. So the remainder r equals p(a)—brilliant! For (x + 2) = (x - (-2)), a = -2; p(-2) = $3*(-2)^3$ - $(-2)^2$ - 7*(-2) + 2 = 3*(-8) - 4 + 14 + 2 = -24 - 4 + 14 + 2, which is (-24 - 4) + (14 + 2) = -28 + 16 = -12. Choice A correctly evaluates p(-2) as -12. Choice B says 12, possibly from changing all signs incorrectly or forgetting the negative in $(-2)^3$, but use parentheses to track signs properly! Sign safety for negatives: when testing (x + 2) = (x - (-2)), you're evaluating at a = -2. Substitute carefully: if p(x) = x³ - 3x + 5, then p(-2) = (-2)³ - 3(-2) + 5 = -8 + 6 + 5 = 3. Use parentheses around negative values to avoid sign errors! This is where most mistakes happen with the Remainder Theorem.
What is the remainder when dividing $p(x)=2x^4-x^2+5$ by $(x+1)$? Use the Remainder Theorem (remainder $=p(a)$ for divisor $(x-a)$).
The remainder is $4$.
The remainder is $8$.
The remainder is $6$.
The remainder is $0$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! The Remainder Theorem states that when you divide a polynomial p(x) by (x - a), the remainder is simply p(a)—just substitute a into the polynomial and evaluate! This works because of how polynomial division works: p(x) = (x - a)·q(x) + r, where r is the remainder. Substituting x = a: p(a) = (a - a)·q(a) + r = 0 + r = r. So the remainder r equals p(a)—brilliant! For (x + 1) = (x - (-1)), a = -1; p(-1) = $2*(-1)^4$ - $(-1)^2$ + 5 = 21 - 1 + 5 = 2 - 1 + 5 = 6. Choice A correctly evaluates p(-1) as 6. Choice B says 4, which could happen if you mistakenly computed $(-1)^4$ as -1 instead of 1, leading to 2(-1) -1 +5 = -2 -1 +5 =2, but remember even powers are positive! Sign safety for negatives: when testing (x + 2) = (x - (-2)), you're evaluating at a = -2. Substitute carefully: if p(x) = x³ - 3x + 5, then p(-2) = (-2)³ - 3(-2) + 5 = -8 + 6 + 5 = 3. Use parentheses around negative values to avoid sign errors! This is where most mistakes happen with the Remainder Theorem.
Verify the claim using the Remainder Theorem: When dividing $p(x)=x^4-3x^2+2x+1$ by $(x-1)$, the remainder is $1$.
False, because $p(1)=0$ so the remainder is $0$.
True, because $p(1)=1$.
True, because $p(-1)=0$.
False, because $p(-1)=1$ so the remainder is $1$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! The Remainder Theorem states that when you divide a polynomial p(x) by (x - a), the remainder is simply p(a)—just substitute a into the polynomial and evaluate! This works because of how polynomial division works: p(x) = (x - a)·q(x) + r, where r is the remainder. Substituting x = a: p(a) = (a - a)·q(a) + r = 0 + r = r. So the remainder r equals p(a)—brilliant! To verify, evaluate p(1): $1^4$ = 1, $-31^2$ = -3, +21 = +2, +1; combine: 1 - 3 = -2, -2 + 2 = 0, 0 + 1 = 1. Choice A correctly verifies it's true because p(1)=1 matches the claimed remainder. Choice B incorrectly claims false with p(1)=0, perhaps from miscalculating 1 -3 +2 +1 as 0 by ignoring the last +1. Using the Remainder Theorem: (1) Identify the divisor (x - a) and extract a (remember: (x + 3) = (x - (-3)), so a = -3), (2) Substitute a for every x in p(x), (3) Calculate carefully (use parentheses for negative values!), (4) That result is your remainder. If it equals 0, (x - a) is a factor! This method is dramatically faster than polynomial long division.
If the remainder when $p(x)=x^3-2x^2+kx-5$ is divided by $(x-1)$ is $3$, find $k$. (Use $ \text{remainder} = p(1) $.)
$k=7$
$k=9$
$k=11$
$k=3$
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! The Remainder Theorem states that when you divide a polynomial p(x) by (x - a), the remainder is simply p(a)—just substitute a into the polynomial and evaluate! This works because of how polynomial division works: $p(x) = (x - a) \cdot q(x) + r$, where r is the remainder. Substituting x = a: $p(a) = (a - a) \cdot q(a) + r = 0 + r = r$. So the remainder r equals p(a)—brilliant! Here, p(1) = 3 and we set it equal to 3: $1^3 - 2(1)^2 + k \cdot 1 - 5 = 1 - 2 + k - 5 = -6 + k = 3$, so $k = 9$. Choice B correctly finds k=9. A distractor like k=7 in choice A might come from misadding -6 + k =3 as k=-3+6=3 or similar arithmetic error. Using the Remainder Theorem: (1) Identify the divisor (x - a) and extract a (remember: $(x + 3) = (x - (-3))$, so a = -3), (2) Substitute a for every x in p(x), (3) Calculate carefully (use parentheses for negative values!), (4) That result is your remainder. If it equals 0, (x - a) is a factor! This method is dramatically faster than polynomial long division.
Is $(x+2)$ a factor of $p(x)=x^3+3x^2-4x-12$? Use the Remainder Theorem / Factor Theorem (i.e., $(x-a)$ is a factor iff $p(a)=0$).
Yes, because $p(-2)=0$.
No, because $p(-2)=8$.
Yes, because $p(2)=0$.
No, because the remainder is $0$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! A special case is the Factor Theorem: (x - a) is a factor of p(x) if and only if p(a) = 0. This means the remainder is zero, so the division is exact with no remainder. We can test potential factors by just evaluating the polynomial—if p(a) = 0, we've found a factor! This beats trial-and-error factoring when testing specific values. For (x + 2) = (x - (-2)), a = -2; p(-2) = $(-2)^3$ + $3*(-2)^2$ - 4*(-2) - 12 = -8 + 3*4 + 8 - 12 = -8 + 12 + 8 - 12, which is (-8 - 12) + (12 + 8) = -20 + 20 = 0. Choice A correctly determines that yes, it is a factor because p(-2) = 0. Choice B says no because p(-2) = 8, which might come from forgetting to include the -12 or mishandling signs, but actually it's 0—keep track of all terms! Sign safety for negatives: when testing (x + 2) = (x - (-2)), you're evaluating at a = -2. Substitute carefully: if p(x) = x³ - 3x + 5, then p(-2) = (-2)³ - 3(-2) + 5 = -8 + 6 + 5 = 3. Use parentheses around negative values to avoid sign errors! This is where most mistakes happen with the Remainder Theorem.
Determine if $x=-1$ is a zero of $$p(x)=x^3+2x^2-x-2.$$ (Use the fact that $x=a$ is a zero iff $p(a)=0$.)
Yes; $p(-1)=0$.
No; $p(1)=-2$.
Yes; $p(1)=0$.
No; $p(-1)=2$.
Explanation
This question tests your understanding of the Remainder Theorem—a powerful shortcut that lets you find the remainder when dividing a polynomial by (x - a) without doing any long division! A special case is the Factor Theorem: (x - a) is a factor of p(x) if and only if p(a) = 0. This means the remainder is zero, so the division is exact with no remainder. We can test potential factors by just evaluating the polynomial—if p(a) = 0, we've found a factor! This beats trial-and-error factoring when testing specific values. To check if x = -1 is a zero of p(x) = x³ + 2x² - x - 2, we evaluate p(-1): p(-1) = (-1)³ + 2(-1)² - (-1) - 2 = -1 + 2(1) + 1 - 2 = -1 + 2 + 1 - 2 = 0. Since p(-1) = 0, x = -1 is indeed a zero! Choice A correctly states that x = -1 is a zero because p(-1) = 0. Using the Remainder Theorem: (1) A zero of p(x) is a value a where p(a) = 0, (2) This also means (x - a) is a factor of p(x), (3) Calculate carefully with parentheses for negative values, (4) If p(a) = 0, you've found both a zero and a factor! This connection between zeros and factors is fundamental in algebra.
If $$p(x) = 2x^3 - 5x^2 + 3x - 7$$ and $$p(2) = -5$$, what can be concluded about the polynomial $$q(x) = p(x) + 5$$?
$$q(x)$$ has remainder $$5$$ when divided by $$(x + 2)$$
$$(x - 2)$$ is a factor of $$q(x)$$
$$(x + 2)$$ is a factor of $$q(x)$$
$$q(x)$$ has remainder $$-5$$ when divided by $$(x - 2)$$
Explanation
Since $$p(2) = -5$$, we have $$q(2) = p(2) + 5 = -5 + 5 = 0$$. By the Remainder Theorem, since $$q(2) = 0$$, the factor $$(x - 2)$$ divides $$q(x)$$ evenly. Choice B is incorrect because it uses $$(x + 2)$$ instead of $$(x - 2)$$. Choice C is wrong because $$q(x)$$ has remainder $$0$$, not $$-5$$, when divided by $$(x - 2)$$. Choice D is incorrect because it involves division by $$(x + 2)$$ and the wrong remainder value.
A polynomial $$f(x)$$ has the property that $$f(-3) = 8$$ and $$f(1) = 0$$. When $$f(x)$$ is divided by $$x^2 + 2x - 3$$, what is the remainder?
$$4x + 12$$
$$-2x + 2$$
$$3x + 9$$
$$2x + 2$$
Explanation
Since $$x^2 + 2x - 3 = (x + 3)(x - 1)$$, when $$f(x)$$ is divided by this quadratic, the remainder must be linear: $$R(x) = ax + b$$. By the Remainder Theorem, $$R(-3) = f(-3) = 8$$ and $$R(1) = f(1) = 0$$. So $$-3a + b = 8$$ and $$a + b = 0$$. Solving: $$b = -a$$ and $$-3a + (-a) = 8$$, so $$-4a = 8$$ and $$a = -2$$, $$b = 2$$. Therefore $$R(x) = -2x + 2$$. The other choices don't satisfy both conditions simultaneously.