calc question differential

Question

Let y=tan(3x+6)

Find the differential dy when x=4 and dx=.1

find the differential dy when x=4 and dx=.2

Answer 1

dy = y'dx = 3sec²(3x + 6)dx = 3sec²(18)·0.1 = 0.688;

dy = y'dx = 3sec²(3x + 6)dx = 3sec²(18)·0.2 = 1.3761.