Suppose \[\frac{1}{x^3-x^2-21x+45}=\frac{A}{x+5}+\frac{B}{x-3} + \frac{C}{(x - 3)^2}\] where a,b,c are real constants. what is a?
Hint:
expand this and see what you get
(x+5)(x-3)^2
