(i) (a2 – b2)2
= (a2)2 – 2(a2) (b2) + (b2)2 (Using identity II)
= a4 – 2a2b2 + b4
(ii) (2n + 5)2 – (2n – 5)2
= {(2n)2 + 2 (2n) (5) + (5)2} – {(2n)2 – 2(2n) (5) + (5)2}
(Using identity I and II)
= (4n2 + 20n + 25) – (4n2 – 20n + 25)
= 4n2 + 20n + 25 – 4n2 + 20n – 25
= 4n2 – 4n2 + 20n + 20n + 25 – 25
= 0 + 40n + 0
= 40n
Alternative Method-
(2n + 5)2 – (2n – 5)2
= {(2n + 5) + (2n – 5)} {(2n + 5) – (2n – 5)}
(Using identity II)
= (4n) (10)
= 40n
(iii) (7m – 8n)2 + (7m + 8n)2
= {(7m)2 – 2(7m) (8n) + (8n)2} + {(7m)2 + 2(7m) (8n) + (8n)2} (Using identity I and II)
= (49m2 – 112mn + 64n2) + (49m2 + 112mn + 64n2)
= 49m2 – 112mn + 64n2 + 49m2 + 112 mn + 64 n2
= 49m2 + 49m2 – 112mn + 112mn + 64m2 + 64n2
= 98m2 + 128n2
(iv) (m2 – n2m)2 + 2m3n2
= [(m2)2 – 2(m2) (n2m) + (n2m)2] + 2m3n2 (Using identity II)
= m4 – 2m3n2 + n4m2 + 2m3n2
= m4 – 2m3n2 + 2m3n2 + n4m2
= m + n4m2