500a-(a-y)*(500-x) = 500a -( 500a -ax -500y + xy)
=ax +500y - xy pas de factorisation possible
(50+100)*(80+x)-(100*x)*2 = 150(80+x) - 200x
=12000+150x -200x
=12000-50x
= 50( 240 - x)
(50*y)*(z*x)-(y*x)/2-(50*2)/2-x*y
=50xyz - xy/2 -50 - xy
=50xyz - 3/2 xy - 50 pas de factorisation possible