a) Ta có : a2x + a2y - 7x - 7y
= a2(x + y) - (7x + 7y)
= a2(x + y) - 7(x + y)
= (x + y)(a2 - 7)
b) Ta có : x3 + y(1 - 3x2) + x(3x2 - 1) - y3
= x3 - y(3x2 - 1) + x(3x2 - 1) - y3
= x3 - y3 + [x(3x2 - 1) - y(3x2 - 1)]
= x3 - y3 - (3x2 - 1)(x - y)
= (x - y)(x2 + xy + y2) - (3x2 - 1)(x - y)
= (x - y)[(x2 + xy + y2) - (3x2 - 1)]
= (x - y)(x2 + xy + y2 - 3x2 + 1)
= (x - y)(-2x2 + xy + y2 + 1)
bài 2:a. \(5x.\left(y^2-2yz+z^2\right)\)
\(=5x.\left(y-z\right)^2\) .......k bít dc chưa
b.\(\left(x^2y-x\right)+\left(xy^2-y\right)\)
\(=x.\left(xy-1\right)+y.\left(xy-1\right)\)
\(=\left(xy-1\right).\left(x+y\right)\)
