Question

If(1+x)^15=sigma r=0-15CrX^r, Then sigma r=2-15(r-1)Cr

Answer 1

Answer:

Solution:

nCrnCr−1=n−r+1Cr⇒15Cr15Cr−1=16−rrnCrnCr−1=n−r+1Cr⇒15Cr15Cr−1=16−rr

∴∑r=115r2∴∑r=115r2(16−rr)=(16−rr)=∑r=115∑r=115 (16r−r2)(16r−r2)

=16×15×162−15×16×316=16×15×162−15×16×316

=680