(1x+1y)(1x−1y)=? (a) (1x2−1y2) (b) (1x2+1y2) (c) (1x2+1y2−1xy) (d) (1x2−1y2+1xy)
(1x+1y)(1x−1y)=(1x)2−(1y)2=1x2−1y2