How do you use u-substitution with 20sin(x^2/35)?

Answer 1

I will assume that you are finding the derivative with respect to x.

let u = x^2/35 or u = (1/35)x^2
let y = sin u

dy/du = cos u , and du/dx = (2/35)x

dy/dx = (dy/du)(du/dx)
= (cos u)(2/35)x
= (2x/35)cos (x^2/35)

your aim will be to reach that final line directly.