Question
If coefficient of (2r+3)th and (r−1)th terms in the expansion of (1+x)15 are equal, then value of r is
Answer: Option A
:
A
15C2r+2 =15Cr−2
But15C2r+2 =15C15−(2r+2) =15C13−2r
⇒15C13−2r =15Cr−2 ⇒ r = 5.
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:
A
15C2r+2 =15Cr−2
But15C2r+2 =15C15−(2r+2) =15C13−2r
⇒15C13−2r =15Cr−2 ⇒ r = 5.
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