Differentiate given problems w.r.t.x.
(5x)3 cos 2x
Let y = (5x)3 cos 2x
Taking log on both sides, we get log y = log (5x)3 cos 2x=3 cos 2x (log 5x) Differentiating w.r.t x. we get
1ydydx=3cos2xddx(log5x)ddx(3cos2x)
=(3cos2x)(55x,5)+(log5x)[3(−sin2x).2]
(Using product ruleddx(u.v)=uddxv+vddxu)
dydx=y{3 cos 2xx−6(sin 2x)(log 5x)}
dydx=(5x)3 cos 2x{3 cos 2xx−6 sin 2x log 5x}