99 Percentile Qs Bank for JEE MainMathematicsBinomial Theorem
If the k^ th term in the expansion of ( 3 2 x^2- 1 3 x )^6 is independent of x , then the numerically greatest term in the expansion of ( 3 2 x^2- 1 3 x )^k when x= 2 3 , is
Options
- A40 81
- B( 7 6 )^5
- C20 27
- D( 7 6 )^4
Correct answer
C. 20 27
Step-by-step solution
We have, k^ th term is the expansion of ( 3 2 x^2- 1 3 x )^6 is independent of x Now, aligned T_ p+1 & = ^6 C_p ( 3 2 )^ 6-p (x)^ 12-2^p (- 1 3 )^p (x^ -p ) T_ p+1 & = ^6 C_p ( 3 2 )^ 6-p (x)^ 12-3 p (- 1 3 )^ aligned T_ p+i is independent of x aligned & 12-3 r & =0, r=4 & k =r+1=5 aligned aligned & Greatest term of ( 3 2 x^2- 1 3 x )^5 & r= [ n+1 1+ | 9 x^3 2 | ]= [ 6 1+ 9 2 8 27 ] [ x= 2 3 ] & r= [ 18 7 ]=2 & T₃= ^5 C₂ ( 3 2 x^2 )^3 (- 1 3 x )^2=10 27 8 x^4 9 & T₃=10 27 8 ( 2 3 )^4 1 9 = 20 27 aligned