linear approximation?

Question

Let f be the function defined by y = f(x)= 4 x^2

1) Find the actual change in y when x changes from 2 to 2.1

2)Use the differential dy of the function f to find the APPROXIMATE change in y when x changes from 2 to 2.1

* i don't need work, just the answer for 1 and 2 is fine

Answer 1

Actual change =4*(2.1)^2-16 =1.64
Using differentials
dy =8x*dx = 16*0.1=1.6

Answer 2

I'm confused when you say change it from 2 to 2.1??

f(x)= 4x^2
f(x)= 4(2.1)^2
f(x)= 4(4.41)
f(x)= 17.64

you don't need the work, just the answers??.....do your own homework.........