Đáp án:
a, ax + bx +ay + by+ b( x+y)
= a( x+y) + b( x+y)
= (x + y) ( a+b)
b, $x^{2}$ y + x$y^{2}$ - x- y
= xy( x+y) -( x+y)
=(x+y)(xy-1)
c, $x^{2}$ + xy -5x - 5y
= x( x+y) -5(x+y)
= (x +y)(x-5)
d, ax +ay -7x - 7y
= a(x+y) -7(x+y)
= (x +y)(a-7)
e, $x^{4}$ +$x^{3}$ +x +1
= $x^{3}$(x+1) + (x+1)
= (x +1)($x^{3}$ +1)
f, 5$x^{2}$ +3(x+y) - 5$y ^{2}$
= 5( $x^{2}$ -$y^{2}$ ) +3(x+y)
=5(x-y)(x+y) + 3(x+y)
= (x+y)(5x-5y+3)