a, \(5y^2-5x^2+6x+6y=5\left(y-x\right)\left(x+y\right)+6\left(x+y\right)\)
\(=\left(x+y\right)\left(5y-5x+6\right)\)
b, \(12x^2+19x+7=12x^2+12x+7x+7\)
\(=12x\left(x+1\right)+7\left(x+1\right)=\left(12x+7\right)\left(x+1\right)\)
5y2 - 5x2 + 6x + 6y
= 5(y2 - x2) + 6(x + y)
= 5(y - x)(x + y) + 6(x + y)
= (x + y)(5y - 5x + 6)
b) 12x2 + 19x + 7
= 12x2 + 12x + 7x + 7
= 12x(x + 1) + 7(x + 1)
= (x + 1)(12x + 7)