A. 8y2 - 10y
= 2y(4y - 5)
B. 3x + 3y + x2 - y2
= 3(x + y) + (x + y)(x - y)
= (x + y)(3 + x - y)
c)
Ta có: \(C=x^2-x-3\)
\(=x^2+2x-3x+3\)
\(=\left(x^2+2x\right)-\left(3x+3\right)\)
\(=x\left(x+1+1\right)-3\left(x+1\right)\)
\(=x+x\left(x+1\right)-3\left(x+1\right)\)
\(=x+\left(x+1\right)\left(x-3\right)\)