Q: Let y = 4 x^2.

Find the change in y, \Delta y when x= 4 and \Delta x = 0.2

Find the differential dy when x= 4 and dx = 0.2

My solution:

dy/dx = 8x

dy = 8x * dx

dy = (8*4)(.2) = 6.4

But 6.4 is the correct answer only for dy and not change of y, ain't they the same thing?