y=cos x3, then dydx=?
none of these
These type of questions are done by substitution.
Put x3=u, differentiating u w.r.t. 'x'
∴ 3x2=dudx .....(i)
Also y=cos u
Now differentiating y w.r.t. u,dydu=−sinu=−sinx3....(ii)
Using (i) and (ii) dydu.dudx=dydx=−3x2sinx3