Step-by-step explanation:
if you mean x multiply 2 :
j(x) = 2x + 1
j(a+1) = 2(a+1) + 1
= 2a+ 2 +1
=2a + 3
if you mean x to the power of 2
j(x) = x^2 +1
j(a+1) = (a+1)^2 + 1
= a^2 + 2a + 1 +1
= a^2 + 2a + 2
