Binomial Theorem 1 Question 11

12. The positive value of λ for which the coefficient of x2 in the expression x2x+λx2 is 720 , is

(a) 3

(b) 5

(c) 22

(d) 4

Show Answer

Answer:

Correct Answer: 12. (a)

Solution:

  1. The general term in the expansion of binomial expression (a+b)n is Tr+1=nCranrbr, so the general term in the expansion of binomial expression x2x+λx2 is

Tr+1=x210Cr(x)10rλx2r10Crx2x10r2λrx2r10Crλrx2+1022r

Now, for the coefficient of x2, put 2+10r22r=2

10r22r=010r=4rr=2

So, the coefficient of x2 is 10C2λ2=720 [given]

10!2!8!λ2=7201098!28!λ2=72045λ2=720λ2=16λ=±4λ=4



जेईई के लिए मॉक टेस्ट

एनसीईआरटी अध्याय वीडियो समाधान

दोहरा फलक