b)x²-y²-7x+7y

=(x²-y²)-(7x-7y)

=(x-y)(x+7)-7(x-y)

=(x-y)[(x+y)-7]

=(x-y)(x+y-7)

Thay x=107;y=7 vào biểu thức ta có:

(107-7)(107+7-7)

=100.107

=10700

\(b.x^2-y^2-7x+7y\)  tại \(x=107\) và \(y=7\)

\(=107^2-7^2-7.107+7.7\)

\(=11449-49-749+49\)

\(=10700\)

Theo mình là như vậy 

Chúc bạn học tốt nha

\(\Leftrightarrow x^2+3x+2-x^2+6x-9=11\)

hay x=2

\(=x^2+8x-x-8=x\left(x+8\right)-\left(x+8\right)=\left(x+8\right)\left(x-1\right)\)

\(x^2+8x-x-8=8\left(x-1\right)+x\left(x-1\right)=\left(8+x\right)\left(x-1\right)\)

   x²+7x-8
= x²-x+8x-8
= (x²-x)+(8x-8)
= x(x-1)+8(x-1)
= (x-1)(x+8)

\(=-5x^2+15x+x-3=-5x\left(x-3\right)+\left(x-3\right)=\left(1-5x\right)\left(x-3\right)\)

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

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

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

\(=x^2+2\cdot6\cdot x+6^2=\left(x+6\right)^2\\ =\left(94+6\right)^2=100^2=10000\)

a. x\(^2\) + 12x + 36 = x\(^2\) + 2 . x . 6 + 6\(^2\) = ( x + 6 )\(^2\)

thay x = 94 vào biểu thức, ta có:

( 94 + 6 )\(^2\) = 100\(^2\) = 10000

vậy x + 12x + 36 = 10000 tại x = 94.

\(a,=3x^2+12x-7x+20+2x^3-3x^2-2x^3-5x=20\)

a. \(x\left(3x+12\right)-\left(7x-20\right)+x^2\left(2x-3\right)-x\left(2x^2+5\right)\\ =\left(3x^2+12x\right)-\left(7x-20\right)+\left(2x^3-3x^2\right)-\left(2x^3+5x\right)\\ =3x^2+12x-7x+20+2x^3-3x^2-2x^3-5x\\ =\left(2x^3-2x^3\right)+\left(3x^2-3x^2\right)+\left(12x-7x-5x\right)+20\\ =0+0+0+20\\ =20\)

\(3x+2\left(5-x\right)=0\Leftrightarrow3x+10-2x=0\Leftrightarrow x=-10\)

\(3x^2-3x\left(x-2\right)=36\\ \Leftrightarrow3x^2-\left(3x^2-6x\right)=36\\ \Leftrightarrow3x^2-3x^2+6x=36\\ \Leftrightarrow6x=36\\ \Leftrightarrow x=36:6\\ \Leftrightarrow x=6\)