How can we write this???
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This is the answer hope it helps you the second one is the one with explanation
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Anonymous:
just see it
it is not a permutation
Up there is n factorial which is n(n-1)(n-2)......3.2.1
And not n(n-1)(n-2)........(n-r).....r8??
yes then there down is also (n-r) factorial which cancel out the upper one
in the set of n numbers there may come r
then we can write factorial n in the form of n(n-1)(n-2)(n-3).......(n-r+2)(n-r+1)(n-r)....(3)(2)(1)
How will u get n-r factorial in numerator
it is the formation of combination that ncr= factorial n/ (factorial r)(factorial n-factorial r)
Leave dude ....u did not understand wat I m asking
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