NCERT Solutions
Class 8 Maths
Algebraic Expressions and Identities

Ex.9.4 Q.3
Simplify:
1. (x2 - 5) × (x + 5) + 25
2. (a2 + 5) × (b2 + 3) + 5
3. (t + s2) × (t2 - s)
4. (a + b) × (c - d) + (a - b) × (c + d) + 2(ac + bd)
5. (x + y) × (2x + y) + (x + 2y) × (x - y)
6. (x + y) × (x2 – xy + y2)
7. (1.5x – 4y) × (1.5x + 4y + 3) – 4.5x + 12y
8. (a + b + c) × (a + b - c)
1. (x2 - 5) × (x + 5) + 25 = x2(x + 5) - 5(x + 5) + 25
= x3 + 5x2 – 5x – 25 + 25
= x3 + 5x2 – 5x
2. (a2 + 5) × (b2 + 3) + 5 = a2(b2 + 3) + 5(b2 + 3) + 5
= a2b2 + 3a2 + 5b2 + 15 + 5
= a2b2 + 3a2 + 5b2 + 20
3. (t + s2) × (t2 - s) = t (t2 - s) + s2(t2 - s)
= t3 – ts + s2 t2 – s3
4. (a + b) × (c - d) + (a - b) × (c + d) + 2(ac + bd)
= a (c - d) + b (c - d) + a (c + d) - b (c + d) + 2ac + 2bd
= ac – ad + bc – bd + ac + ad – bc – bd + 2ac + 2bd
= ac + ac + 2ac – bd – bd + bc – bc – ad + ad + 2bd
= 4ac
5. (x + y) × (2x + y) + (x + 2y) × (x - y)
= x (2x + y) + y (2x + y) + x (x - y) + 2y (x - y)
= 2x2 + xy + 2xy + y2 + x2 – xy + 2xy – 2y2
= 3x2 + 4xy – y2
6. (x + y) × (x2 – xy + y2) = x (x2 – xy + y2) + y (x2 – xy + y2)
= x3 – x2 y + xy2 + x2 y – xy2 + y3
= x3 + y3
7. (1.5x – 4y) × (1.5x + 4y + 3) – 4.5x + 12y
= 1.5x(1.5x + 4y + 3) – 4y (1.5x + 4y + 3) – 4.5x + 12y
= 2.25x2 + 6.0xy + 4.5x – 6.0xy – 16y2 – 12y – 4.5x + 12y
= 2.25x2 – 16y2
8. (a + b + c) × (a + b - c) = a (a + b - c) + b (a + b - c) + c (a + b - c)
= a2 + ab – ac + ab + b2 – bc + ac + bc – c2
= a2 + b2 – c2 + 2ab