Tamil Nadu Board of Secondary EducationHSC Science Class 11

Prove that nCnnnn2nCn=2n×1×3×...(2n-1)n! - Mathematics

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Sum

Prove that `""^(2"n")"C"_"n" = (2^"n" xx 1 xx 3 xx ... (2"n" - 1))/("n"!)`

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Solution

L.H.S = `""^(2"n")"C"_"n"`

= `(2"n"!)/("n"!(2"n" - "n")!) = (2"n"!)/("n"!"n"!)`

= `((2"n")(2"n" - 1)(2"n" - 2)(2"n" - 3)  ... 4*3*2*1)/("n"!"n"!)`

Numerator has n tems in wich n tems are even and n tems are odd.

Taking one 2 from the n even terms we get

= `(2("n")(2"n" - 1)(2)("n" - 1)(2"n" - 3)  ...  2(2)*3*2(2)*1)/("n"!"n"!)`

= `(2^"n"[("n")("n" - 1)("n" - 2)  .... 2*1][(2"n" -1)(2"n" - 3) .....3*1])/("n"!"n"!)`

= `(2^"n" xx "n"! (2"n" - 1(2"n" - 3)  .... 3*1))/("n"!"n"!)`

= `(2^"n" xx 1 xx 3 xx 5 ... (2"n" - 3)(2"n" - 1))/("n"!)`

= R.H.S

Concept: Combinations
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Chapter 4: Combinatorics and Mathematical Induction - Exercise 4.3 [Page 186]

APPEARS IN

Tamil Nadu Board Samacheer Kalvi Class 11th Mathematics Volume 1 and 2 Answers Guide
Chapter 4 Combinatorics and Mathematical Induction
Exercise 4.3 | Q 7 | Page 186

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