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If, for a positive integer n , the quadr...

If, for a positive integer `n ,` the quadratic equation, `x(x+1)+(x-1)(x+2)++(x+ n-1)(x+n)=10 n` has two consecutive integral solutions, then `n` is equal to : ` (1) 10` (2) `11` (3) `12` (4) `9`

A

11

B

12

C

9

D

10

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The correct Answer is:
A
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ALLEN-SEQUENCE AND PROGRESSION-Exercise (JM)
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  9. If a,b and c be three distinct real numbers in G.P and a+b+c=xb, then ...

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  16. Let the sum of the first n terms of a non-constant A.P., a(1), a(2), a...

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  18. Let numbers a(1),a(2)…a(16) are in AP and a(1)+a(4)+a(7)+a(10)+a(13)+a...

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  19. If alpha and beta are the roots of the equation 375 x^(2) - 25x - 2 = ...

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