Question

Answer 1

Bài 2 :

a)\(B=-2x^2\cdot\left(1-x\right)+4\cdot\left(x^2+5-x^3\right)=-2x^2+2x^2+4x^2+20-4x^3=4x^2+20-4x^3.\)

b) 

Answer 2

b) \(C=x\cdot\left(2x-3\right)-4\cdot\left(10-x\right)=2x^2-3x-40+4x=2x^2+x-40\)

Answer 3

c) \(D=y\left(3x+5y\right)-7x\left(y-1+2x\right)=3xy+5y^2-7xy+7x-14x=5y^2-4xy-7x\)

Answer 4

d) \(M=\left(x+2\right)\left(x-5\right)+\left(1-x\right)\left(x-3\right)=x^2-5x+2x-10+1x-3-x^2+3x\\ =\left(x^2-x^2\right)+\left(-5x+2x+1x+3x\right)+\left(-10-3\right)=x-13\)

Answer 5

e) \(N=\left(x^2-3x-2\right)\left(x-1\right)-x\left(2x+1\right)=x^3-x^2-3x^2+3-2x+2-2x^2+x\\ =x^3-6x^2+5\)

Answer 6

f) \(P=\left(2-5x\right)3x-\left(x+2\right)\left(x-2\right)=6x-15x^2-\left[x^2-4\right]=6x-15x^2-x^2+4\\ =6x-14x^2+4\)

Answer 7

Bài 3 :

\(P=\left(2-5x\right)3x-\left(x+2\right)\left(x-2\right)+14x^2=\left[\left(2-5x\right)3x-\left(x+2\right)\left(x-2\right)\right]+14x\\ =6x-14x^2+4+14x^2=6x+4\left(1\right)\)

Thay x=-4 vào (1) ta được : \(6x+4=6\cdot\left(-4\right)+4=-24+4=-20\)

Vậy P=-20