Page 29 - Mathematics Class - IX

Viva-Voce

1. Factorise a + b .
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Ans. a + b = (a + b) (a – ab + b )
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2. Using identity a + b = (a + b) (a – ab + b ), find the value of 6 + 2 .
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Ans. (6 + 2) (6 – 6 × 2 + 2 ) = 8 × 28 = 224
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3. Express a + b in terms of (a + b) .
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Ans. a + b = (a + b) – 3ab (a + b)
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4. Write the possible expression for the dimensions of a cuboid whose volume is 5x – 20x.
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Ans. 5x – 20x = 5x (x – 2) (x + 2)
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5. Find the real zero of a + 1.
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Ans. a + 1 = 0 ⇒ a = –1 ⇒ a = (–1) ⇒ a = –1
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6. Evaluate 2 × 16 by using the identity a + b = (a + b) (a + b – ab)
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Ans. 2 × 16 = 16 + 16 = (16 + 16) (16 + 16 – 16 × 16)
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(32) (256) = 8192
7. Write the real zero of x + 1?
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Ans. x + 1 = 0
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or x = –1 ⇒ x = (–1) 3
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or x = –1
MCQs
1. The factors of 27p + 125 are
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a) (3p + 5) b) (3p + 5) (9p – 15p + 25)
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c) (3p – 5) d) (3p – 5p + 25)p
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2. Write the zeroes of (125 y + 1)
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1 −1
a) 5 b) c) d) None of these
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3. The degree of (4 + y) (16 + y – 4y) is
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a) 2 b) 1 c) 3 d) 4
4. Value of 12 + 5 is
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a) 1583 b) 1853 c) 1358 d) 1385
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Answers: 1. b) (3p + 5) (9p – 15p + 25) 2. c)
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5
3. c) 3 4. b) 1853
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