If f(a)=a^2, what is the value of (f(a-b)−f(a))/b ?  Choose the correct choice from the following options:
A) a
B) b
C) 2a
D) -2a + b
E) 2b - a
start with f(a+b) before start calculations: f(a-b)=(a-b)^2= a^2-2ab+b^2   a^2-2ab+b^2 - a^2/b = (simplify a^2)   -2ab+b^2/b = (cancel b's)   = -2a+b   Ans : -2a + b
<result>D</result>
If f(a)=a^2, what is the value of (f(a-b)−f(a))/b ?