We have,
(i) 16a2−254a2
=(4a)2−(52a)2=(4a+52a)(4a−52a)
(ii) 16a2b−b16a2=b(16a2−116a2)
=b{(4a)2−(14a)2}
=b(4a+14a)(4a−14a)
(iii) 100(x+y)2−81(a+b)2={10(x+y)}2−{9(a+b)}2
={10(x+y)+9(a+b)}{10(x+y)−9(a+b)}
=(10x+10y+9a+9b)(10x+10y−9a−9b)
(iv) (x−1)2−(x−2)2={(x−1)+{(x−2)}{(x−1)−(x−2)}
=(2x−3)(x−1−x+2)
=(2x−3)×1
=2x−3