First, we factor the denominator:
x2+3x−18=(x+6)(x−3) Now we can write the partial fraction decomposition as:
(x+6)(x−3)8x−12=x+6A+x−3B To find A and B, we multiply both sides by (x+6)(x−3): 8x−12=A(x−3)+B(x+6) We can solve for A and B by choosing convenient values for x.
8(3)−12=A(3−3)+B(3+6) 24−12=0+9B B=912=34 8(−6)−12=A(−6−3)+B(−6+6) −48−12=−9A+0 A=−9−60=320 Thus, the partial fraction decomposition is:
x2+3x−188x−12=x+6320+x−334=3(x+6)20+3(x−3)4