If the coefficients of the rth and (r+1)th term in the expansion of (3+7x) raised to power 29 are equal, then r=..?

Dear student,

I will give u a hint here:

Expansion (x+y)ⁿ :

(i)        There are (n+1) terms in the expansion.

(ii)        In each term, sum of the indices of ‘x’ and ‘y’ is equal to ‘n’.

(iii)        In any term, the lower suffix of ‘c’ is equal to the index of ‘y’, and the index of x = n-(lower suffix of c).

(iv)             Because  ⁿC_r = ⁿC_n-r,

    so we have :

ⁿC_o = ⁿC_n

ⁿC₁=ⁿC_n-1

ⁿC₂=ⁿC_n-2 etc.

It follows that the coefficients of terms equidistant from the beginning and the ends are equal.

Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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Sagar Singh

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