Question

cần gấp ạ

Answer 1

Bài 10:

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

\(=2x^2+3x-10x-15-2x^2+6x+x+7\)

\(=\left(2x^2-2x^2\right)+\left(3x-10x+6x+x\right)+\left(-15+7\right)\)

=0+0-8

=-8

=>Biểu thức này không phụ thuộc vào biến

Bài 11:

a: \(\left(x+6\right)\left(x+8\right)-x^2=20\)

=>\(x^2+8x+6x+48-x^2=20\)

=>14x+48=20

=>14x=20-48=-28

=>x=-2

b: \(\left(x+1\right)\left(x+2\right)-\left(x-3\right)\left(x+4\right)=6\)

=>\(x^2+2x+x+2-\left(x^2+4x-3x-12\right)=6\)

=>\(x^2+3x+2-\left(x^2+x-12\right)=6\)

=>\(x^2+3x+2-x^2-x+12=6\)

=>2x+14=6

=>2x=-8

=>x=-4

c: \(2\left(3x+2\right)\left(x-4\right)-3\left(2x-1\right)\left(x+2\right)=-5\)

=>\(2\left(3x^2-12x+2x-8\right)-3\left(2x^2+4x-x-2\right)=-5\)

=>\(2\left(3x^2-10x-8\right)-3\left(2x^2+3x-2\right)=-5\)

=>\(6x^2-20x-16-6x^2-6x+4=-5\)

=>-26x-12=-5

=>-26x=-5+12=7

=>\(x=-\frac{7}{26}\)

Bài 9:

a: \(2x\left(6x-1\right)-3x\left(4x-1\right)\)

\(=12x^2-2x-\left(12x^2-3x\right)\)

\(=12x^2-2x-12x^2+3x=x\)

b: \(\left(x+1\right)\left(x^2-x+1\right)+\left(x-1\right)\left(x^2+x+1\right)\)

\(=x^3+1+x^3-1\)

\(=2x^3\)

c: \(2\left(3x-1\right)\left(2x+5\right)-\left(4x-1\right)\left(3x-2\right)\)

\(=2\left(6x^2+15x-2x-5\right)-\left(12x^2-8x-3x+2\right)\)

\(=2\left(6x^2+13x-5\right)-\left(12x^2-11x+2\right)\)

\(=12x^2+26x-10-12x^2+11x-2=37x-12\)

d: \(\left(x-2\right)\left(x^2+x+1\right)-x\left(x^2-1\right)\)

\(=\left(x-1\right)\left(x^2+x+1\right)-\left(x^2+x+1\right)-x\left(x^2-1\right)\)

\(=x^3-1-\left(x^2+x+1\right)-x^3+x\)

\(=x-1-x^2-x-1=-x^2-2\)

Bài 8:

a: \(\left(x-1\right)\left(x^2+x+1\right)\)

\(=x^3+x^2+x-x^2-x-1\)

\(=x^3-1\)

b: \(\left(x+1\right)\left(x^2-x+1\right)\)

\(=x^3-x^2+x+x^2-x+1\)

\(=x^3+1\)