Respuesta :

firstly chain rule is dy/dx = dy/du * du/dx

a) y = 5u² + u - 1 hence dy/du = 10u +1

u = 3x +1 hence du/dx = 3

so dy/dx = 3(10u +1) {sub in u and expand}

b) y= u^-2 hence dy/du = -2u^-3

u=2x+3 hence du/dx = 2

so dy/dx= 2(-2u^-3) {sub in u}