Question

The sum of the co-efficients of all odd degree terms in the expansion of $${\left( {x + \sqrt {{x^3} - 1} } \right)^5} + {\left( {x - \sqrt {{x^3} - 1} } \right)^5},\left( {x > 1} \right)$$         is:

A. $$0$$
B. $$1$$
C. $$2$$  
D. $$- 1$$
Answer :   $$2$$
Solution :
Since we know that,
$$\eqalign{ & {\left( {x + a} \right)^5} + {\left( {x - a} \right)^5} \cr & = 2\left[ {^5{C_0}{x^5} + {\,^5}{C_2}{x^3} \cdot {a^2} + {\,^5}{C_4}x \cdot {a^4}} \right] \cr & \therefore \,\,{\left( {x + \sqrt {{x^3} - 1} } \right)^5} + {\left( {x - \sqrt {{x^3} - 1} } \right)^5} \cr & = 2\left[ {^5{C_0}{x^5} + {\,^5}{C_2}{x^3}\left( {{x^3} - 1} \right) + {\,^5}{C_4}x{{\left( {{x^3} - 1} \right)}^2}} \right] \cr & = 2\left[ {{x^5} + 10{x^6} - 10{x^3} + 5{x^7} - 10{x^4} + 5x} \right] \cr} $$
∴ Sum of co-efficients of odd degree terms = 2.

Releted MCQ Question on
Algebra >> Binomial Theorem

Releted Question 1

Given positive integers $$r > 1, n > 2$$   and that the co - efficient of $${\left( {3r} \right)^{th}}\,{\text{and }}{\left( {r + 2} \right)^{th}}$$    terms in the binomial expansion of $${\left( {1 + x} \right)^{2n}}$$  are equal. Then

A. $$n = 2r$$
B. $$n = 2r + 1$$
C. $$n = 3r$$
D. none of these
Releted Question 2

The co-efficient of $${x^4}$$ in $${\left( {\frac{x}{2} - \frac{3}{{{x^2}}}} \right)^{10}}$$   is

A. $$\frac{{405}}{{256}}$$
B. $$\frac{{504}}{{259}}$$
C. $$\frac{{450}}{{263}}$$
D. none of these
Releted Question 3

The expression $${\left( {x + {{\left( {{x^3} - 1} \right)}^{\frac{1}{2}}}} \right)^5} + {\left( {x - {{\left( {{x^3} - 1} \right)}^{\frac{1}{2}}}} \right)^5}$$       is a polynomial of degree

A. 5
B. 6
C. 7
D. 8
Releted Question 4

If in the expansion of $${\left( {1 + x} \right)^m}{\left( {1 - x} \right)^n},$$    the co-efficients of $$x$$ and $${x^2}$$ are $$3$$ and $$- 6\,$$ respectively, then $$m$$ is

A. 6
B. 9
C. 12
D. 24

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