Cách 1:
\(f\left(x\right)=\left(x^2-7x\right)\left(4x^3-2x^2-5x\right)=4x^5-30x^4+9x^3+35x^2\)
\(f'\left(x\right)=20x^4-120x^3+27x^2+70x\)
Cách 2:
\(f\left(x\right)=\left(x^2-7x\right)\left(4x^3-2x^2-5x\right)\)
\(f'\left(x\right)=\left(x^2-7x\right)'\left(4x^3-2x^2-5x\right)+\left(x^2-7x\right)\left(4x^3-2x^2-5x\right)'\)
\(f'\left(x\right)=\left(2x-7\right)\left(4x^3-2x^2-5x\right)+\left(x^2-7x\right)\left(12x^2-4x-5\right)\)
Bla bla.... Tự tách ra
\(f'\left(x\right)=20x^4-120x^3+27x^2+70\)