Calculus helpp, confused

Question

Question 1

Let y = 2x ^ 2

Find the change in y Delta*y when x = 4 and Az = 0.2

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

Question 2

Let y= tan(2x + 3)

Find the differential dy when x = 1 and dx = 0.2

Find the differential dy when x = 1 and dx = 0.4

Answer 1

y' = dy/dx

y' = 4x

dy/dx = 4x

dy = 4 x dx

= 4 * 4 * 0.2

= 16 * 0.2

= 3.2

likewise

dy = sec^2(2x+3) * 2 * dx

= sec^2 (2*1+3) * 2 * 0.2

= sec^2(5) * 0.4