Math Problem Statement

the polynomial p(x)=2x^4+ax^3+bx-1 when p(x) is divided by x^2-x+1 the remainder is 3x+2 find a and b

Solution

We are given the polynomial p(x)=2x4+ax3+bx1p(x) = 2x^4 + ax^3 + bx - 1, and the fact that when it is divided by x2x+1x^2 - x + 1, the remainder is 3x+23x + 2. We need to find the values of aa and bb.

Step 1: Division Structure

The division of p(x)p(x) by x2x+1x^2 - x + 1 follows the structure:

p(x)=(x2x+1)q(x)+(3x+2)p(x) = (x^2 - x + 1)q(x) + (3x + 2)

Where q(x)q(x) is the quotient, and 3x+23x + 2 is the remainder.

Step 2: Express the Polynomial

Write out p(x)=(x2x+1)q(x)+(3x+2)p(x) = (x^2 - x + 1)q(x) + (3x + 2). Here, we want to match the degrees of the polynomial on both sides. Since the degree of p(x)p(x) is 4, the degree of q(x)q(x) should be 2, so assume:

q(x)=px2+qx+rq(x) = px^2 + qx + r

Thus, we have:

p(x)=(x2x+1)(px2+qx+r)+(3x+2)p(x) = (x^2 - x + 1)(px^2 + qx + r) + (3x + 2)

Step 3: Expand the Product

Now, expand (x2x+1)(px2+qx+r)(x^2 - x + 1)(px^2 + qx + r):

(x2x+1)(px2+qx+r)=x2(px2+qx+r)x(px2+qx+r)+(px2+qx+r)(x^2 - x + 1)(px^2 + qx + r) = x^2(px^2 + qx + r) - x(px^2 + qx + r) + (px^2 + qx + r)

Expand each term:

  1. x2(px2+qx+r)=px4+qx3+rx2x^2(px^2 + qx + r) = px^4 + qx^3 + rx^2
  2. x(px2+qx+r)=px3qx2rx-x(px^2 + qx + r) = -px^3 - qx^2 - rx
  3. (px2+qx+r)=px2+qx+r(px^2 + qx + r) = px^2 + qx + r

Now combine the terms:

p(x)=px4+(qp)x3+(rq+p)x2+(r+q)x+rp(x) = px^4 + (q - p)x^3 + (r - q + p)x^2 + (-r + q)x + r

Step 4: Match Coefficients

Next, match the coefficients of this expansion with the terms of p(x)=2x4+ax3+bx1p(x) = 2x^4 + ax^3 + bx - 1.

From the x4x^4 term: p=2p = 2

From the x3x^3 term: qp=aq2=aq=a+2q - p = a \quad \Rightarrow \quad q - 2 = a \quad \Rightarrow \quad q = a + 2

From the x2x^2 term: rq+p=0r(a+2)+2=0r=ar - q + p = 0 \quad \Rightarrow \quad r - (a + 2) + 2 = 0 \quad \Rightarrow \quad r = a

From the x1x^1 term: q+r=b(a+2)+a=bb=2-q + r = b \quad \Rightarrow \quad -(a + 2) + a = b \quad \Rightarrow \quad b = -2

From the constant term: r=1a=1r = -1 \quad \Rightarrow \quad a = -1

Step 5: Final Values

Thus, we have:

a=1andb=2a = -1 \quad \text{and} \quad b = -2

Conclusion:

The values of aa and bb are a=1\boxed{a = -1} and b=2\boxed{b = -2}.


Would you like a more detailed explanation of any part of the solution?

Here are some related questions to explore:

  1. What is the quotient q(x)q(x) in this division?
  2. How do we verify the remainder using synthetic or polynomial division?
  3. What happens when we change the divisor to a higher-degree polynomial?
  4. How would the solution differ if the remainder was a constant?
  5. Can this method be extended to non-polynomial divisors?

Tip: Always check your result by substituting the values of aa and bb back into the original polynomial to verify consistency with the remainder.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Polynomial Division
Remainder Theorem
Algebra

Formulas

p(x) = (divisor) * (quotient) + remainder
p(x) = (x^2 - x + 1)(px^2 + qx + r) + (3x + 2)

Theorems

Remainder Theorem
Polynomial Division

Suitable Grade Level

Grades 10-12