If a/(x-2)+b/(x+3)=(2x+11)/(x^2+x-6)ax2+bx+3=2x+11x2+x6, then (a,b) = ?

1 Answer
Dec 7, 2017

3/(x-2)-1/(x+3)3x21x+3

Explanation:

This can be solvec by using partial fractions.

We know that (2x+11)/(x^2+x-6)=a/(x-2)+b/(x+3)2x+11x2+x6=ax2+bx+3

We can add these two fractions to get:
a/(x-2)+b/(x+3)=(a(x+3))/((x-2)(x+3))+(b(x-2))/((x-2)(x+3))ax2+bx+3=a(x+3)(x2)(x+3)+b(x2)(x2)(x+3)
=(a(x+3)+b(x-2))/((x+3)(x-2))=a(x+3)+b(x2)(x+3)(x2)

By multiplying by (x-3)(x+2)(x3)(x+2), we get:

2x+11=a(x+3)+b(x-2)2x+11=a(x+3)+b(x2)

First, we will use x=2x=2 as this will cancel out bb and allow us to work out aa.

2(2)+11=a(2+3)+b(2-2)2(2)+11=a(2+3)+b(22)

4+11=a(5)+b(0)4+11=a(5)+b(0)

15=5a15=5a

a=15/5=3a=155=3

Now, we do the same for x=-3x=3

2(-3)+11=a(-3+3)+b(-3-2)2(3)+11=a(3+3)+b(32)

-6+11=a(0)+b(-5)6+11=a(0)+b(5)

5=-5b5=5b

b=-5/5=-1b=55=1

a=3,b=-1a=3,b=1

(2x+11)/(x^2+x-6)=3/(x-2)+(-1)/(x+3)2x+11x2+x6=3x2+1x+3

=3/(x-2)-1/(x+3)=3x21x+3