Question

(x+y) (a+b)-(y+z) (a+b)

Answer 1

(x+y)(a+b)-(y+z)(a+b)

first we solve half

(x+y)(a+b)

(xa+xb+ya+yb)

(y+z)(a+b)

(ya+yb+za+zb)

(xa+xb+ya+yb)-(ya+yb+za+zb)

xa+xb+ya+yb-ya-yb-za-zb

which needs to cut

+ya-ya+yb-yb

now left

xa+xb-za-zb

x (a+b)-z (a+b)

(x-z)(a+b)2