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If `a_1,a_2, a_3, a_4`be the coefficient of four consecutive terms in the expansion of `(1+x)^n ,`then prove that: `(a_1)/(a_1+a_2)+(a_3)/(a_3+a_4)=(2a_2)/(a_2+a_3)dot` |
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Answer» First four coefficient terms of `(1+x)^n` are, `1, C(n,1), C(n,2),C(n,3)` `:. a_1 = 1` `a_2 = n` `a_3 = (n(n-1))/2` `a_4 = (n(n-1)(n-2))/6` Now, `L.H.S. = a_1/(a_1+a_2) + a_3/(a_3+a_4)` `=1/(n+1) +( (n(n-1))/2)/( (n(n-1))/2+ (n(n-1)(n-2))/6)` `=1/(n+1) +(1/(1+((n-2))/3))` `=1/(n+1)+3/(n+1) = 4/(n+1)` Now, `R.H.S. = (2a_2)/(a_2+a_3)` `=(2n)/(n+(n(n-1))/2)` `=(2*2)/(2+n-1)` `=4/(n+1)` `:. L.H.S. = R.H.S.` |
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