Question 758410
f(x)=x^2+1


f(a+1)=(a+1)^2+1 ... replace ALL copies of 'x' with 'a+1'


f(a+1)=(a+1)(a+1)+1


f(a+1)=a(a+1)+1(a+1)+1


f(a+1)=a^2+a+a+1+1


f(a+1)=a^2+2a+2


So the answer is f(a+1)=a^2+2a+2