Advertisements
Advertisements
Question
Find the middle term (terms) in the expansion of `(3x - x^3/6)^9`
Advertisements
Solution
Given expression is `(3x - x^3/6)^9`
Number of terms = 9 + 1 = 10 ....(even)
∴ Middle terms are `n^"th"/2` term and `(n/2 + 1)^"th"` term
= `10^"th"/2`
= 5th term and (5 + 1) = 6th term
General Term `"T"_(r + 1) = ""^n"C"_r x^(n - r) y^r`
∴ T5 = `"T"_(4 + 1)`
= `""^9"C"_4 (3x)^(9 - 4) (- x^3/6)^4`
= `""^9"C"_4 (3)^5 * x^5 (-1/6)^4 * x^12`
= `(9 xx 8 xx 7 xx 6)/(4 xx 3 xx 2 xx 1) xx (3 xx 3 xx 3 xx 3 xx 3)/(6 xx 6 xx 6 xx 6) x^17`
= `189/8 x^17`
Now, T6 = T5+1
= `""^9"C"_5 (3x)^(9 - 5) (- x^3/6)^5`
= `""^9"C"_5 (3)^4 x^4 (- 1/6)^5 * x^15`
= `(9 xx 8 xx 7 xx 6 xx 5)/(5 xx 4 xx 3 xx 2 xx 1) (3)^4 (- 1/6)^5 * x^19`
= ` - 21/16 x^19`
Hence, the required middle terms are `189/8 x^17` and `- 21/16 x^19`
APPEARS IN
RELATED QUESTIONS
Write the general term in the expansion of (x2 – y)6
Write the general term in the expansion of (x2 – yx)12, x ≠ 0
Find the middle terms in the expansions of `(3 - x^3/6)^7`
In the expansion of (1 + a)m + n, prove that coefficients of am and an are equal.
Prove that the coefficient of xn in the expansion of (1 + x)2n is twice the coefficient of xn in the expansion of (1 + x)2n–1 .
Find the middle term in the expansion of:
(iv) \[\left( \frac{x}{a} - \frac{a}{x} \right)^{10}\]
Find the middle terms in the expansion of:
(ii) \[\left( 2 x^2 - \frac{1}{x} \right)^7\]
Find the middle terms(s) in the expansion of:
(i) \[\left( x - \frac{1}{x} \right)^{10}\]
Find the middle terms(s) in the expansion of:
(ii) \[\left( 1 - 2x + x^2 \right)^n\]
Find the middle terms(s) in the expansion of:
(iv) \[\left( 2x - \frac{x^2}{4} \right)^9\]
Find the middle terms(s) in the expansion of:
(v) \[\left( x - \frac{1}{x} \right)^{2n + 1}\]
Find the middle terms(s) in the expansion of:
(vii) \[\left( 3 - \frac{x^3}{6} \right)^7\]
Find the term independent of x in the expansion of the expression:
(i) \[\left( \frac{3}{2} x^2 - \frac{1}{3x} \right)^9\]
Find the term independent of x in the expansion of the expression:
(x) \[\left( \frac{3}{2} x^2 - \frac{1}{3x} \right)^6\]
If the coefficients of 2nd, 3rd and 4th terms in the expansion of (1 + x)2n are in A.P., show that \[2 n^2 - 9n + 7 = 0\]
If in the expansion of (1 + x)n, the coefficients of pth and qth terms are equal, prove that p + q = n + 2, where \[p \neq q\]
In the expansion of (1 + x)n the binomial coefficients of three consecutive terms are respectively 220, 495 and 792, find the value of n.
If in the expansion of (1 + x)n, the coefficients of three consecutive terms are 56, 70 and 56, then find n and the position of the terms of these coefficients.
If the 6th, 7th and 8th terms in the expansion of (x + a)n are respectively 112, 7 and 1/4, find x, a, n.
Find the sum of the coefficients of two middle terms in the binomial expansion of \[\left( 1 + x \right)^{2n - 1}\]
If A and B are the sums of odd and even terms respectively in the expansion of (x + a)n, then (x + a)2n − (x − a)2n is equal to
The number of irrational terms in the expansion of \[\left( 4^{1/5} + 7^{1/10} \right)^{45}\] is
If the sum of odd numbered terms and the sum of even numbered terms in the expansion of \[\left( x + a \right)^n\] are A and B respectively, then the value of \[\left( x^2 - a^2 \right)^n\] is
The middle term in the expansion of \[\left( \frac{2x}{3} - \frac{3}{2 x^2} \right)^{2n}\] is
Find the middle term (terms) in the expansion of `(p/x + x/p)^9`.
If the term free from x in the expansion of `(sqrt(x) - k/x^2)^10` is 405, find the value of k.
If p is a real number and if the middle term in the expansion of `(p/2 + 2)^8` is 1120, find p.
In the expansion of `(x^2 - 1/x^2)^16`, the value of constant term is ______.
If the expansion of `(x - 1/x^2)^(2n)` contains a term independent of x, then n is a multiple of 2.
If the 4th term in the expansion of `(ax + 1/x)^n` is `5/2` then the values of a and n respectively are ______.
The coefficient of y49 in (y – 1)(y – 3)(y – 5) ...... (y – 99) is ______.
The middle term in the expansion of (1 – 3x + 3x2 – x3)6 is ______.
Let for the 9th term in the binomial expansion of (3 + 6x)n, in the increasing powers of 6x, to be the greatest for x = `3/2`, the least value of n is n0. If k is the ratio of the coefficient of x6 to the coefficient of x3, then k + n0 is equal to ______.
Let the coefficients of the middle terms in the expansion of `(1/sqrt(6) + βx)^4, (1 - 3βx)^2` and `(1 - β/2x)^6, β > 0`, common difference of this A.P., then `50 - (2d)/β^2` is equal to ______.
The sum of the real values of x for which the middle term in the binomial expansion of `(x^3/3 + 3/x)^8` equals 5670 is ______.
