Question

If f(x)=3x+1 then f(a+h)-f(a)

Answer 1

f(x) = 3x+1
put x = a+h
f(a+h)  = 3(a+h) + 1
f(a+h) = 3a + 3h + 1
put x = a
f(a) = 3a + 1
f(a+h)-f(a) = 3a + 3h + 1 -(3a+1)
f(a+h)-f(a) = 3a +3h + 1 - 3a -1
f(a+h)-f(a) = 3h