(i)

[(a + b)^{2} = a^{2 }+ 2ab + b^{2}]

= 4/9m^{2} + 2mn + 9/4n^{2}

(v) (0.4p − 0.5q)^{2}

= (0.4p)^{2} − 2 (0.4p) (0.5q) + (0.5q)^{2} [(a − b)^{2} = a^{2} − 2ab + b^{2}]

= 0.16p^{2} − 0.4pq + 0.25q^{2}

(vi) (2xy + 5y)^{2}

= (2xy)^{2} + 2(2xy) (5y) + (5y)^{2} [(a + b)^{2} = a^{2} + 2ab + b^{2}]

= 4x^{2}y^{2} + 20xy^{2 }+ 25y^{2}