We have, f(x)=x5−5x4+5x3−10 f′(x)=5x4−20x3+15x2 For maxima or minima put f′(x)=0 ∴ 5x4−20x3+15x2=0 ⇒ 5x2(x2−4x+3)=0 ⇒5x2(x−3)(x−1)=0 x=0,1,3 f′′(x)=20x3−60x2+30x f′′(x)=10x(2x2−6x+3) f′′(0)=0 f′′(1)=10(2−6+3)<0 f′′(3)=30(18−18+3)>0 ∴ Local maxima at x=1 and local minima at x=3 Here, a=1,b=3 ∴ 2a+b=2+3=5