(i)
[(a + b)2 = a2 + 2ab + b2]
= 4/9m2 + 2mn + 9/4n2
(v) (0.4p − 0.5q)2
= (0.4p)2 − 2 (0.4p) (0.5q) + (0.5q)2 [(a − b)2 = a2 − 2ab + b2]
= 0.16p2 − 0.4pq + 0.25q2
(vi) (2xy + 5y)2
= (2xy)2 + 2(2xy) (5y) + (5y)2 [(a + b)2 = a2 + 2ab + b2]
= 4x2y2 + 20xy2 + 25y2