Bonsoir
[tex]500a-(a-y)(500-x) \\ =500a-(500a-ax-500y+xy) \\ =500a-500a+ax+500y-xy \\ =ax-xy+500y \\ =(a-y)x+500y [/tex]
[tex](50+100)(80+x)-(100x)2 \\ =4000+50x+8000+100x-200x \\ =-50x+12000[/tex]
[tex](50y)(zx)- \frac{yx}{2} - \frac{100}{2} -xy \\ =50yzx- \frac{yx-100}{2}-xy [/tex]