Class 8 Maths
Algebraic Expressions and Identities
Ex.9.1 Q.1
Identify the terms, their coefficients for each of the following expressions:
1. 5xyz2 - 3zy
2. 1+ x + x2
3. 4x2 y2 - 4x2 y2 z2
4. 3 - pq + qr - rp
5. +
– xy
6. 0.3a – 0.6ab + 0.5b
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Ex.9.1 Q.2
Classify the following polynomials as monomials, binomials, trinomials.
Which polynomials do not fit in any of these three categories:
1. x + y,
2. 1000,
3. x + x2 + x3 + x4,
4. 7 + y + 5x,
5. 2y – 3y2,
6. 2y - 3y + 4y,
7. 5x – 4y + 3xy,
8. 4z – 15z2,
9. ab + bc + cd + da,
10. pqr,
11. p2 q + pq2,
12. 2p + 2q
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Ex.9.1 Q.3
Add the following:
1. ab – bc, bc – ca, ca - ab
2. a - b + ab, b - c + bc, c - a + ac
3. 2p2 q2 - 3pq + 4, 5 + 7pq - 3p2 q2
4. l2 + m2, m2 + n2, n2 + l2 + 2lm + 2mn + 2nl
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Ex.9.1 Q.4
(a) Subtract: 4a – 7ab + 3b + 12 from 12a – 9ab + 5b - 3
(b) Subtract: 3xy + 5yz - 7zx from 5xy – 2yz – 2zx + 10xyz
(c) Subtract: 4p2 q - 3pq + 5pq2 - 8p + 7q – 10 from 18 – 3p – 11p + 5pq – 2pq2 + 5p2 q
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Ex.9.2 Q.1
Find the product of the following pairs of monomials:
1. 4,7p
2. -4p, 7p
3. -4p, 7pq
4. 4p3, -3p
4. 4p, 0
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Ex.9.2 Q.2
Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively:
1. (p, q),
2. (10m, 5n),
3. (20x2, 5y2),
4. (4x, 3x),
5. (3mn, 4np)
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Ex.9.2 Q.3
Complete the table of products:
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Ex.9.2 Q.4
Obtain the volume of rectangular boxes with the following length, breadth and height respectively:
1. 5a, 3a2, 7a4
2. 2p, 4q, 8r
3. xy, 2x2 y, 2xy2
4. a, 2b, 3c
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Ex.9.2 Q.5
Obtain the product of:
1. xy, yz, zx
2. –a, a2, a3
3. 2, 4y, 8y2, 16y3
4. a, 2b, 3c, 6abc
5. m, -mn, mnp
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Ex.9.3 Q.1
Carry out the multiplication of the expressions in each of the following pairs:
1. 4p, q + r
2. ab, a - b
3. a + b, 7a2 b2
4. a2 - 9, 4a
5. pq + qr + rp, 0
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Ex.9.3 Q.2
Complete the table:
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Ex.9.3 Q.3
Find the product:
1. a2 × 2a22 × 4a26
2. (2xy ÷ 3) × (-9x2 y2 ÷ 10)
3. (-10pq3 ÷ 3) × (6p3 q ÷ 5)
4. x × x2 × x3 × x4
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Ex.9.3 Q.4
(a) Simplify: 3x (4x - 5) + 3 and find values for 1. x = 3 2. x = 1/2
(b) Simplify: a (a2 + a + 1) + 5 and find its value for 1. a = 0 2. a =1 3. a = -1.
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Ex.9.3 Q.5
(a) Add: p (p - q), q (q - r) and r (r – p)
(b) Add: 2x (z - x – y) and 2y (z -y – zx)
(c) Subtract: 3l (l - 4m + 5n) from 4l (10n – 3m + 2l)
(d) Subtract: 3a (a + b + c) – 2b (a – b + c) from 4c (-a + b + c)
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Ex.9.4 Q.1
Multiply the binomial
1. (2x + 5) and (4x - 3)
2. (y - 8) and (3y - 4)
3. (2.5l – 0.5m) and (2.5l + 0.5m)
4. (a + 3b) and (x + 5)
5. (2pq + 3q2) and (3pq – 2q2)
6. ((3a2 ÷ 4) + 3b2) and 4(a2 – (2b2 ÷ 3))
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Ex.9.4 Q.2
Find the product:
1. (5 – 2x) × (3 + x)
2. (x + 7y) × (7x - y)
3. (a2 + b) × (a + b2)
4. (p2 – q2) × (2p + q)
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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)
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Ex.9.5 Q.1
Use a suitable identity to get each of the following products:
1. (x + 3) × (x + 3)
2. (2y + 5) × (2y + 5)
3. (2a - 7) × (2a - 7)
4. (3a – ) × (3a –
)
5. (1.1m – 0.4) × (1.1m + 0.4)
6. (a2 + b2) × (-a2 + b2)
7. (6x - 7) × (6x + 7)
8. (-a + c) × (-a + c)
9. ( +
) × (
+
)
10. (7a – 9b) × (7a – 9b)
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Ex.9.4 Q.2
Use the identity (x + a) (x + b) = x2 + (a + b) x + ab to find the following products:
1. (x + 3) (x + 7)
2. (4x + 5) (4x + 1)
3. (4x - 5) (4x - 1)
4. (4x + 5) (4x - 1)
5. (2x + 5y) (2x + 3y)
6. (2a2 + 9) (2a2 + 5)
7. (xyz - 4) (xyz - 2)
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Ex.9.5 Q.3
Find the following squares by using identities:
1. (b - 7)2
2. (xy + 3z)2
3. (6x2 – 5y)2
4. ( +
)2
5. (0.4p – 0.5q)2
6. (2xy + 5y)2
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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
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Ex.9.5 Q.5
Show that:
1. (3x + 7)2 – 84x = (3x - 7)2
2. (9p – 5q)2 + 180pq = (9p + 5q)2
3. (4 – 3
)2 + 2mn = 16
+ 9
4. (4pq + 3q)2 - (4pq - 3q)2 = 48pq2
5. (a - b) (a + b) + (b - c) (b + c) + (c - a) (c + a) = 0
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Ex.9.5 Q.6
Using identities, evaluate:
1. 712
2. 992
3. 1022
4. 9982
5. 5.22
6. 297 × 303
7. 78 × 82
8. 8.92
9. 1.05 × 9.5
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Ex.9.5 Q.7
Using a2 – b2 = (a + b) (a - b), find:
1. 512 – 492
2. (1.02)2 – (0.98)2
3. 1532 – 1472
4. 12.12 – 7.92
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Ex.9.5 Q.8
Using (x + a) (x + b) = x2 + (a + b) x + ab, find
1. 103 × 104
2. 5.1 × 5.2
3. 103 × 98
4. 9.7 × 9.8
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