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If sum of the series a- (a+d) + (a+ 2d)-...

If sum of the series `a- (a+d) + (a+ 2d)- (a + 3d) +`….up to 21 terms is

A

`-10d`

B

`a+20d`

C

`a+10d`

D

20d

Text Solution

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The correct Answer is:
C
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Knowledge Check

  • The sum of the series 2^(2) + 2(4^(2)) + 3(6^(2)) + ….upto 10 terms is

    A
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    B
    11200
    C
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    D
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    A
    `(-1)^(n-1) (n(n+1))/(2)`
    B
    `n(n+1)`
    C
    `-(n+1)n`
    D
    `(n(n+1)(2n+1))/(6)`

  • Consider the following differential equations. D_(1) : y=4 (dy)/(dx) + 3x (dy)/(dy) , D_(2), (d ^(2)y)/(dx ^(2))= (3+ ((dy)/(dx)) ^(2) )^(4/3)D_(3):[1+ ((dy)/(dx))]^(2) = ((dy)/(dx)) ^(2) The ratio of the sum of the orders of D_(1),D_(2)and D_(3) to the sum of their degrees is

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    D
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