\(x^2-y^2+8x+6y+7\)
\(=\left(x-y\right)\left(x+y\right)+7\left(x+y\right)+x-y+7\)
\(=\left(x+y\right)\left(x-y+7\right)+\left(x-y+7\right)\)
\(=\left(x+y+1\right)\left(x-y+7\right)\)
Ta có x2 - y2 + 8x + 6y + 7
= x2 + 8x + 16 - y2 + 6y - 9
= \(x^2+4x+4x+16-y^2+3y+3y-9\)
= x(x + 4) + 4(x + 4) - y(y - 3) + 3(y - 3)
= (x + 4)2 - (y - 3)2
= (x + 4 + y - 3)(x + 4 - y + 3)
= (x + y + 1)(x - y + 7)