NCERT Solutions
Class 8 Maths
Algebraic Expressions and Identities

Ex.9.5 Q.4
Simplify:
1. (a2 – b2)2
2. (2x + 5)2 – (2x - 5)2
3. (7m – 8n)2 + (7m + 8n)2
4. (4m + 5n)2 + (5m + 4n)2
5. (2.5p – 1.5q)2 – (1.5p – 2.5q)2
6. (ab + bc)2 – 2ab2 c
7. (m2 – n2 m2) + 2m3 n2
1. (a2 – b2)2 = (a2)2 – 2 × a2 × b2 + (b2)2
[Using (a - b)2 = a2 - 2ab + b2]
= a4 – 2a2 b2 + b4
2. (2x + 5)2 – (2x - 5)2 = (2x)2 + 2 × 2x × 5 + (5)2 - {(2x)2 + 2 × 2x × 5 + (5)2}
= 4x2 + 20x + 25 – (4x2 - 20x + 25)
= 4x2 + 20x + 25 – 4x2 + 20x - 25
= 40x
3. (7m – 8n)2 + (7m + 8n)2
= (7m)2 - 2 × 7m × 8n + (8n)2 + {(7m)2 + 2 × 7m × 8n + (8n)2}
= 49m2 – 112mn + 64n2 + (49m2 + 112mn + 64n2)
= 49m2 – 112mn + 64n2 + 49m2 + 112mn + 64n2
= 98m2 + 128n2
4. (4m + 5n)2 + (5m + 4n)2
= (4m)2 + 2 × 4m × 5n + (5n)2 + {(5m)2 + 2 × 5m × 4n + (4n)2}
= 16m2 + 40mn + 25n2 + 25m2 + 40mn + 16n2
= 41m2 + 80mn + 41n2
5. (2.5p – 1.5q)2 – (1.5p – 2.5q)2
= (2.5p)2 - 2 × 2.5p × 1.5q + (1.5q)2 - {(1.5p)2 - 2 × 1.5p × 2.5q + (2.5q)2}
= 6.25p2 – 7.50pq + 2.25q2 – (2.2.5p2 – 7.50pq + 6.25q2)
= 6.25p2 – 7.50pq + 2.25q2 – 2.2.5p2 + 7.50pq - 6.25q2
= 4p2 – 4q2
6. (ab + bc)2 – 2ab2 c = (ab)2 + 2 × ab × bc + (bc)2 – 2ab2 c
= a2 b2 + 2ab2 c + b2 c2 - 2ab2 c
= a2 b2 + b2 c2
7. (m2 – n2 m) + 2m3 n2 = (m2)2 – 2 × m2 × n2 m + (n2 m)2 - 2m3 n2
= m4 – 2m3 n2 + n4 m2 - 2m3 n2
= m4 + n4 m2