Math Problem Statement

Find a and b if(x+1) (x-1) are the factors of 2x^3-ax^2+bx-5

Solution

Given that (x+1)(x+1) and (x1)(x-1) are factors of the polynomial 2x3ax2+bx52x^3 - ax^2 + bx - 5, we can use the fact that if xcx - c is a factor of a polynomial P(x)P(x), then P(c)=0P(c) = 0.

Step 1: Apply the Factor Theorem

Since (x+1)(x+1) is a factor, substituting x=1x = -1 into the polynomial should give us 0:

P(1)=2(1)3a(1)2+b(1)5=0P(-1) = 2(-1)^3 - a(-1)^2 + b(-1) - 5 = 0

Simplify this:

2ab5=0-2 - a - b - 5 = 0

ab=7    a+b=7(1)- a - b = 7 \implies a + b = -7 \quad (1)

Similarly, since (x1)(x-1) is a factor, substituting x=1x = 1 should also give us 0:

P(1)=2(1)3a(1)2+b(1)5=0P(1) = 2(1)^3 - a(1)^2 + b(1) - 5 = 0

Simplify this:

2a+b5=02 - a + b - 5 = 0

a+b=3(2)-a + b = 3 \quad (2)

Step 2: Solve the System of Equations

We now have a system of two equations:

  1. a+b=7a + b = -7
  2. a+b=3-a + b = 3

Add these two equations together:

(a+b)+(a+b)=7+3(a + b) + (-a + b) = -7 + 3

2b=4    b=22b = -4 \implies b = -2

Substitute b=2b = -2 into equation (1):

a+(2)=7a + (-2) = -7

a=5a = -5

Step 3: Conclusion

The values of aa and bb are:

a=5,  b=2\boxed{a = -5, \; b = -2}

Would you like to know more about polynomial factorization or any other topic? Here are some related questions:

  1. How to factor polynomials completely?
  2. What is the Factor Theorem, and how is it used?
  3. How do you solve a system of linear equations?
  4. What are some practical applications of polynomials in real life?
  5. How to find the roots of a cubic polynomial?

Tip: Always double-check your substitution and simplification steps to avoid errors when solving equations!

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Math Problem Analysis

Mathematical Concepts

Algebra
Polynomials
Factor Theorem
Systems of Equations

Formulas

Factor Theorem: If (x - c) is a factor of a polynomial P(x), then P(c) = 0
System of Equations: Solving for unknown variables using two linear equations

Theorems

Factor Theorem

Suitable Grade Level

Grades 10-12