I need calculus help.

Find the differential of the function y=x3sin(6x).
i found that to be 2sec^2(x) which is correct.
next i need to Evaluate dy and Δy when x=π/4 and dx=−0.2

what is dy: and Δy:

Question

I need calculus help.

Find the differential of the function y=x3sin(6x).
i found that to be 2sec^2(x) which is correct.
next i need to Evaluate dy and Δy when x=π/4 and dx=−0.2 

what is dy: and Δy:

zepdrix · Answer

$$\large y=x^3 \sin(6x)$$Applying the product rule gives us,
$$\large dy=\left[3x^2\sin(6x)+6x^3\cos(6x)\right]dx$$

Hmm I don't quite understand how you got to 2sec^2(x).