Question

f(x)=x^2+4x ,求(f(a+h)-f(a))/h.此题答案是2a+h+4,

Answer 1

f(x)=x^2+4x

f(a+h)=(a+h)^2+4a+4h

f(a)=a^2+4a

f(a+h)-f(a)=a^2+2ah+h^2+4a+4h-a^2-4a

=2ah+h^2+4h

所以：（f(a+h)-f(a)）/h=2a+h+4