We need to apply the chain rule twice.
Recall that the chain rule states, if we have some function f(g(x))f(g(x)), the derivative of ff with respect to xx is equal to the derivative of ff with respect to gg, multiplied by the derivative of gg with respect to xx.
So in this case, the derivative dy/dxdydx will equal the derivative of sin(tan 2x)sin(tan2x) with respect to tan 2xtan2x (basically, treat tan 2xtan2x as a whole variable) times the derivative of tan 2xtan2x with respect to xx.
Derivative of sinsin is just coscos:
dy/dx = cos(tan 2x) * d/dx[tan 2x]dydx=cos(tan2x)⋅ddx[tan2x]
Derivative of tantan is sec^2sec2. However, we need to apply the chain rule again, meaning this time we will just pull the derivative of 2x2x out. (which is just 22)
dy/dx = cos(tan 2x) * sec^2(2x) * 2dydx=cos(tan2x)⋅sec2(2x)⋅2