Question

Answer 1

c) Ta có:

\(\left(7x+1\right)x^2+5x\left(2x^2-\dfrac{1}{5}x-1\right)\)

\(=7x^3+x^2+10x^3-x^2-5x\)

\(=\left(7x^3+10x^3\right)+\left(x^2-x^2\right)-5x\)

\(=17x^3-5x\)

Thay x=-20 vào biểu thức ta có:

\(17\cdot\left(-20\right)^3-5\cdot\left(-20\right)\)

\(=-135900\)

Answer 2

A=7x^3+x^2+10x^3-x^2-5x

=17x^3-5x

Khi x=-20 thì A=17*(-20)^3-5*(-20)

=-135900