1.(x+y)²-4(x+y-1) =(x+y)²-4(x+y)+4=(x+y-2)²2.(ax+by)²-(bx+ay)²=(ax)²+(by)²+2abxy- (bx)²-(ay)²-2abxy=(ax)²-(ay)² - [(bx)²-(by)²]=a&#...