i. Here, a = x, b = y
(x + y)(x – y) = x2 – y2 …. [(a + b)(a – b) = a2 – b2 ]
ii. Here, a = 3x, b = 5
(3x – 5) (3x + 5) = (3x)2 – 52 …. [(a + b)(a – b) = a2 – b2 ]
= 9x2 – 25
iii. Here, A = a, B = 6
(a + 6) (a – 6) = a2 – 62 …. [(A + B)(A – B) = A2 – B2 ]
= a2 – 36
iv. Here, a = x/2 , b = 6
(x/5 + 6) (x/5 - 6) = (x/5)2 - (6)2…. [(a + b)(a – b) = a2 – b2 ]
= x2 /25 - 36