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Polynomial Roots: all problems

Focus mode: every practice problem from the chapter, one after another.

0 / 16 solved

Problem 14.4.1

AMC 10

This problem also appears in the book as 13.2.8.

Let ff be a function for which f(x3)=x2+x+1f\left(\frac{x}{3}\right) = x^2 + x + 1. Find the sum of all values of zz for which f(3z)=7f(3z) = 7.

Problem 14.4.2

AIME

This problem also appears in the book as 13.2.12.

Suppose that the roots of x3+3x2+4x−11=0x^3 + 3x^2 + 4x - 11 = 0 are aa, bb, and cc, and that the roots of x3+rx2+sx+t=0x^3 + rx^2 + sx + t = 0 are a+ba + b, b+cb + c, and c+ac + a. Find tt.

Problem 14.4.3

AMC 10

This problem also appears in the book as 13.2.13.

For certain real numbers aa, bb, and cc, the polynomial

g(x)=x3+ax2+x+10g(x) = x^3 + ax^2 + x + 10

has three distinct roots, and each root of g(x)g(x) is also a root of the polynomial

f(x)=x4+x3+bx2+100x+c.f(x) = x^4 + x^3 + bx^2 + 100x + c.

What is f(1)f(1)?

Problem 14.4.4

AMC 10/12

Let P(x)P(x) be a polynomial with rational coefficients such that when P(x)P(x) is divided by the polynomial x2+x+1x^2 + x + 1, the remainder is x+2x + 2, and when P(x)P(x) is divided by the polynomial x2+1x^2 + 1, the remainder is 2x+12x + 1. There is a unique polynomial of least degree with these two properties. What is the sum of the squares of the coefficients of that polynomial?

Problem 14.4.5

AMC 10

Let P(x)P(x) be the unique polynomial of minimal degree with the following properties:

  • P(x)P(x) has leading coefficient 11,
  • 11 is a root of P(x)−1P(x) - 1,
  • 22 is a root of P(x−2)P(x - 2),
  • 33 is a root of P(3x)P(3x), and
  • 44 is a root of 4P(x)4P(x).

The roots of P(x)P(x) are integers, with one exception. The root that is not an integer can be written as mn\frac{m}{n}, where mm and nn are relatively prime positive integers. What is m+nm + n?

Problem 14.4.6

AMC 12Challenge

Polynomials P(x)P(x) and Q(x)Q(x) each have degree 33 and leading coefficient 11, and their roots are all elements of {1,2,3,4,5}\{1, 2, 3, 4, 5\}. The function f(x)=P(x)Q(x)f(x) = \frac{P(x)}{Q(x)} has the property that there exist real numbers a<b<c<da < b < c < d such that the set of all real numbers xx such that f(x)≤0f(x) \le 0 consists of the closed interval [a,b][a, b] together with the open interval (c,d)(c, d). How many functions f(x)f(x) are possible?

Problem 14.5.1(additional)

AHSME

Given the equations x2+kx+6=0x^2 + kx + 6 = 0 and x2−kx+6=0x^2 - kx + 6 = 0. If, when the roots of the equation are suitably listed, each root of the second equation is 55 more than the corresponding root of the first equation, then kk equals:

Problem 14.5.2(additional)

AMC 10

What is the product of all the roots of the equation

5∣x∣+8=x2−16?\sqrt{5|x| + 8} = \sqrt{x^2 - 16}?

Problem 14.5.3(additional)

AHSME

Let P(x)P(x) be a polynomial such that when P(x)P(x) is divided by x−19x - 19, the remainder is 9999, and when P(x)P(x) is divided by x−99x - 99, the remainder is 1919. What is the remainder when P(x)P(x) is divided by (x−19)(x−99)(x - 19)(x - 99)?

P(19) = 99 and P(99) = 19, so the remainder mod (x - 19)(x - 99) is -x + 118

P(x)=(x−19)(x−99) Q(x)+(ax+b)P(x) = (x - 19)(x - 99)\,Q(x) + (ax + b)
Known: P(19)=99, P(99)=19P(19) = 99,\ P(99) = 19
(19, 99)(99, 19)
    Remainder = ax + b

    At x = 19 and x = 99 the product term is 0, so P and the remainder agree there: the remainder is the line through the two points.

    Step 0 of 4: the remainder is a line ax + b through two known points.

    Problem 14.5.4(additional)

    AIME

    The real root of the equation 8x3−3x2−3x−1=08x^3 - 3x^2 - 3x - 1 = 0 can be written in the form a3+b3+1c\frac{\sqrt[3]{a} + \sqrt[3]{b} + 1}{c}, where aa, bb, and cc are positive integers. Find a+b+ca + b + c.

    Problem 14.5.5(additional)

    AIME

    Let x1<x2<x3x_1 < x_2 < x_3 be the three real roots of the equation 2014 x3−4029x2+2=0\sqrt{2014}\,x^3 - 4029x^2 + 2 = 0. Find x2(x1+x3)x_2(x_1 + x_3).

    Problem 14.5.6(additional)

    AMC 12

    The graph of y=x6−10x5+29x4−4x3+ax2y = x^6 - 10x^5 + 29x^4 - 4x^3 + ax^2 lies above the line y=bx+cy = bx + c except at three values of xx, where the graph and the line intersect. What is the largest of these values?

    Problem 14.5.7(additional)

    AIMEChallenge

    This problem also appears in the book as 12.6.25.

    The equation 2000x6+100x5+10x3+x−2=02000x^6 + 100x^5 + 10x^3 + x - 2 = 0 has exactly two real roots, one of which is m+nr\frac{m + \sqrt{n}}{r}, where mm, nn and rr are integers, mm and rr are relatively prime, and r>0r > 0. Find m+n+rm + n + r.

    Problem 14.5.8(additional)

    AIMEChallenge

    Let P(x)P(x) be a nonzero polynomial such that (x−1)P(x+1)=(x+2)P(x)(x - 1)P(x + 1) = (x + 2)P(x) for every real xx, and (P(2))2=P(3)\left(P(2)\right)^2 = P(3). Then P(72)=mnP\left(\frac{7}{2}\right) = \frac{m}{n}, where mm and nn are relatively prime positive integers. Find m+nm + n.

    Problem 14.5.9(additional)

    AIMEChallenge

    Let P(x)P(x) be a quadratic polynomial with complex coefficients whose x2x^2 coefficient is 11. Suppose the equation P(P(x))=0P(P(x)) = 0 has four distinct solutions, x=3,4,a,bx = 3, 4, a, b. Find the sum of all possible values of (a+b)2(a + b)^2.

    Problem 14.5.10(additional)

    AMC 10Challenge

    A quadratic polynomial with real coefficients and leading coefficient 11 is called disrespectful if the equation p(p(x))=0p(p(x)) = 0 is satisfied by exactly three real numbers. Among all the disrespectful quadratic polynomials, there is a unique such polynomial p~(x)\tilde{p}(x) for which the sum of the roots is maximized. What is p~(1)\tilde{p}(1)?