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Consider the following statements . I....

Consider the following statements .
I. The coefficient of the middle term in th expansion of `( 1+ x)^(8)` is equal to the middle term of `( x + ( 1)/( x))^(8)`
II. The coefficient of the middle term in the expansion of `( 1+ x)^(8)` is less than the coefficient of the fifth term in the expansion of `( 1+ x)^(7)` ?
What of the above statements is `//` are correct ?

A

I only

B

II only

C

Both I and II

D

Neither I nor II

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the two statements given and determine their correctness based on the binomial theorem. ### Step 1: Find the middle term in the expansion of \((1 + x)^8\) The formula for the \(r\)-th term in the expansion of \((a + b)^n\) is given by: \[ T_{r} = \binom{n}{r-1} a^{n-(r-1)} b^{(r-1)} \] In the case of \((1 + x)^8\), the middle term occurs when \(r = \frac{8}{2} + 1 = 5\) (since \(n\) is even). Thus, the middle term is: \[ T_{5} = \binom{8}{4} (1)^{8-4} (x)^{4} = \binom{8}{4} x^4 \] Calculating \(\binom{8}{4}\): \[ \binom{8}{4} = \frac{8!}{4!4!} = \frac{8 \times 7 \times 6 \times 5}{4 \times 3 \times 2 \times 1} = 70 \] So, the middle term in the expansion of \((1 + x)^8\) is \(70x^4\). ### Step 2: Find the middle term in the expansion of \((x + \frac{1}{x})^8\) For the expression \((x + \frac{1}{x})^8\), we again find the middle term when \(r = 5\): \[ T_{5} = \binom{8}{4} x^{8-4} \left(\frac{1}{x}\right)^{4} = \binom{8}{4} x^{4} \cdot \frac{1}{x^4} = \binom{8}{4} \] Calculating \(\binom{8}{4}\) again gives us: \[ \binom{8}{4} = 70 \] Thus, the middle term in the expansion of \((x + \frac{1}{x})^8\) is also \(70\). ### Conclusion for Statement I Both middle terms are equal to \(70\). Therefore, **Statement I is correct**. ### Step 3: Find the fifth term in the expansion of \((1 + x)^7\) For the expression \((1 + x)^7\), we find the fifth term where \(r = 5\): \[ T_{5} = \binom{7}{4} (1)^{7-4} (x)^{4} = \binom{7}{4} x^4 \] Calculating \(\binom{7}{4}\): \[ \binom{7}{4} = \frac{7!}{4!3!} = \frac{7 \times 6}{2 \times 1} = 21 \] Thus, the fifth term in the expansion of \((1 + x)^7\) is \(21x^4\). ### Conclusion for Statement II We compare the coefficients: - The coefficient of the middle term in \((1 + x)^8\) is \(70\). - The coefficient of the fifth term in \((1 + x)^7\) is \(21\). Since \(70\) is not less than \(21\), **Statement II is incorrect**. ### Final Answer - Statement I is correct. - Statement II is incorrect.
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