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If the three consecutive in the expansio...

If the three consecutive in the expansion of `(1+x)^n` are 28, 56, and 70, then the value of `n` is.

A

`(ac+ab+bc)/(b^(2)+ac)`

B

`(2ac+ab+bc)/(b^(2) - ac)`

C

`(ab+ac)/(b^(2) - ac)`

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
B
Here, `a = .^(n)C_(r) , b = .^(n)C_(r+1)` and `c = .^(n)C_(r+2)`.
Put `n = 2,r = 0` , then option (2) holds the condition, i.e,
`n = (2ac+ab+bc)/(b^(2)-ac)`
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CENGAGE-BINOMIAL THEOREM-Exercise (Single)
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  2. If ^n+1C(r+1) : ^n Cr : ^(n-1)C(r-1)=11 :6:3, then n r =

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  3. If the three consecutive in the expansion of (1+x)^n are 28, 56, and 7...

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  4. Which term in the expansion of (2-3x)^(19) has algebrically the last c...

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  5. The value of ("^n C0)/n+("^nC1)/(n+1)+("^nC2)/(n+2)+....+("^nC n)/(2n)...

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  6. The value of sum(r=1)^n(-1)^(r+1)(^^n C r)/(r+1) is equal to -1/(n+1) ...

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  7. If sum(r=0)^(10)((r+2)/(r+1))^^n Cr=(2^8-1)/6 , then n is 8 b. 4 c. 6 ...

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  8. The value ofsum(r=0)^(10) (-1)^(r).4^(10-r)""^(30)C(r)""^(30-r)C(10-r)...

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  9. The value ofunderset(r=0)overset(10)sumr^(10)C(r),3^(r).(-2)^(10-r) is...

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  10. ""^(15)C(0)=

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  11. If (1+x)^n=C0+C1x+C2x^2++Cn x^n ,t h e nC0C2+C1C3+C2C4++C(n-2)Cn= ((2...

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  12. ^404C4-^303C4.^4C1+^202C4.^4C2-^101C4.^4C3=

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  13. The value of sum(r=0)^(40) r""^(40)C(r)""^(30)C(r) is

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  14. The value of sum(r=0)^(50)(-1)^r(^(50)Cr)/(r+2) is equal to 1/(50xx51)...

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  15. (n+2)nC0(2^(n+1))-(n+1)nC1(2^(n))+(n)nC2(2^(n-1))-.... is equal to

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  16. The value of sum(r=0)^(50)(-1)^r(^(50)Cr)/(r+2) is equal to 1/(50xx51)...

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  17. sum(r=0)^(300)ar x^r=(1+x+x^2+x^3)^(100)dot If a=sum(r=0)^(300)ar ,t ...

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  18. sum(r=0)^(300)ar x^r=(1+x+x^2+x^3)^(100)dot If a=sum(r=0)^(300)ar ,t ...

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  19. The value of sum(r=0)^(20)r(20-r)(^(20)Cr)^2 is equal to 400^(39)C(20)...

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  20. Iff(x) =.^(40)C(1).x(1-x)^(39) + 2..^(40)C(2)x^(2)(1-x)^(38)+3..^(40)C...

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