AP EAMCET2014MathematicsBinomial Theorem
The term independent of x in the expansions of ( x - 2 x )¹⁸ is
Options
- A- ¹⁸ C₉ 2^9
- B¹⁸ C₉ 2¹²
- C¹⁸ C₆ 2^6
- D¹⁸ C₆ 2^8
Correct answer
A. - ¹⁸ C₉ 2^9
Step-by-step solution
General term in the expansion of ( x - 2 x )¹⁸ is aligned T_ r+1 & = ¹⁸ C_r( x )^ 18-r (- 2 x )^r & = ¹⁸ C_r(x)^ 18-r 2 (-2)^r(x)^ - r 2 & = ¹⁸ C_r(-2)^r x^ 9-r aligned For independent of x , array rlrl & put 9-r & =0 & & r & =9 & & T₁₀ & = ¹⁸ C₉(-2)^9 & =- ¹⁸ C₉ 2^9 array