(i) We have,
(4x+2y)2=(4x)2+2×(4x)×(2y)+(2y)2
[Using: (a+b)2=a2+2ab+b2]
=16x2+16xy+4y2
(ii) We have,
(5x−y)2=(5x)2−2×(5x)×(y)+(y)2
[Using: (a−b)2=a2−2ab+b2]
=252−10xy+y2
(iii) We have,
(3x+7y)(3x−7y)=(3x2−(7y)2
[Using: (a+b)(a−b)=a2−b2]
(3x+7y)(3x−7y)=9x2−49y2