Question Bank - Mathematics

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Consider the following statements in respect of the expansion of (x + y)101. Among all the coefficients of the terms, the coefficient of the 6th term has the highest value2. The coefficient of the 3rd term is equal to coefficient of the 9th termWhich of the above statements is /are correct ?

A.
1 only
B.
2 only
C.
Both 1 and 2
D.
Neither 1 nor 2

Solution:

Concept:1). In the expansion of (x + y)n, the term having the greatest coefficient is the middle term.2). When n is even, the middle term is \(\displaystyle \frac{n+2}{2}\) and the greatest coefficient is nCn/23). When n is odd, the middle term is \(\displaystyle \frac{n+1}{2}\) or \(\displaystyle \frac{n+3}{2}\) and the greatest coefficient is \(\displaystyle ^nC_{\frac{n-1}{2}}\) or \(\displaystyle ^nC_{\frac{n+1}{2}}\)4). rth term for the binomial expression, (x + y)n, Tr = nCr-1 xn-r-1 yr-1Calculation:The given expansion is (x + y)10Statement I: Among all the coefficients of the terms, the coefficient of the 6th term has the highest valueThe value of n is 10 which is even. So, the term having the greatest coefficient is the \(\displaystyle \frac{n+2}{2}\) = \(\displaystyle \frac{10+2}{2}\) = 6? The coefficient of the 6th term has the highest value.Statement II: The coefficient of the 3rd term is equal to the coefficient of the 9th term.We know that, \(^nC_r=\frac{n!}{r!(n-r)!}\)The coefficient of the 3rd term, T3 = 10C2 = \(\frac{10!}{8!.2!}\)The coefficient of the 9th term, T9 = 10C8 = \(\frac{10!}{8!.2!}\) ? Coefficient of the 3rd term = Coefficient of the 9th term.? Both Statement I and II are correct.

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