Question

Answer 1

\(a,A=3x\left(2x+1\right)-\left(6x+1\right)\left(x-3\right)\\ =6x^2+3x-6x^2+18x-x+3\\ =20x+3\)

Thay \(x=-4\) vào \(20x+3\Rightarrow A=20.\left(-4\right)+3=-77\)

\(b,B=\left(x+2\right)\left(x-2\right)\left(x+1\right)-x\left(x^2-4\right)\\ =\left(x+1\right)\left(x^2-4\right)-x\left(x^2-4\right)\\ =\left(x^2-4\right)\left(x+1-x\right)\\ =x^2-4\)

Thay \(x=10\) vào \(x^2-4\Rightarrow B=10^2-4=96\)