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in Mathematics by (71.2k points)

The Co-efficient of xr in expansion of S =(x+3)n-1 + (x+3)n-2 (x+2) + (x+3)n-3 (x+2)2 +...+ (x+2)n-1 is.................... 

(a) nCr (3r - 2r

(b) nCr (3n-r-2n-r)

(c) 3n-r- 2n-r 

(d) 3n-r + 2n-r

1 Answer

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Best answer

Correct option: (b) nCr (3n-r-2n-r)

Explanation:

= (3+x)n - (2+x)n 

∴ coefficient of xrnCr (3n-r-2n-r)

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