f(x)=(x^3+1)(2x^2+8x-5),
=> f(x)=2x^5+8x^4-5x^3+2x^2+8x-5
求导
f'(x) = 2×5x^(5-1) + 8×4x^3 - 15x^2 + 4x + 8
= 10x^4 + 32x^3 - 15x^2 +4x + 8