hiiiiiiiiiiiiii

if ever you'll get a 4 degree equation in jee to solve,then it will be an easy one and you'll need to apply hit n trial method.

it can be clearly seen that x=1 satisfies the eqn.

always try using x=-2,-1,0,1,2

any one will definitely satisfy any  four  degree eqn given in jee.

but if u want the proper way ,then hit_ur_heart has explained the right way correctly.

but just a little correction,in this case f"(x)=12x^2 but not 12x^3