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If C(18,r)=C(18,r+2), find C(r,5)....

If `C(18,r)=C(18,r+2)`, find `C(r,5)`.

Text Solution

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Given
`18_(C_r)​=18_(C_(r+2))`
​ So,` r=r+2` or `18−r=r+2`
`16=2r`
or,` r=8`
So, `8_(C_5)​=(8!​)/(5!3!)=(6x7xx8)/6​=56`
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