Maharashtra State BoardHSC Science (General) 11th
Advertisement Remove all ads

Select the correct answer from the given alternatives. If the coefficient of x2 and x3 in the expansion of (3 + ax)9 are the same, then the value of a is - Mathematics and Statistics

MCQ

Select the correct answer from the given alternatives.

If the coefficient of x2 and x3 in the expansion of (3 + ax)9 are the same, then the value of a is

Options

  • `-7/9`

  • `-9/7`

  • `7/9`

  • `9/7`

Advertisement Remove all ads

Solution

`9/7`

Explanation;

tr+1= 9Cr(3)9–r(ax)r = 9Cr39–rarxr

9C2 × 37 × a2 = 9C3 × 36 × a3

∴ `(9!)/(2!7!) xx 3 = (9!)/(3!6!) xx "a"`

∴ a = `9/7`

Concept: Middle term(s) in the expansion of (a + b)n
  Is there an error in this question or solution?
Advertisement Remove all ads

APPEARS IN

Balbharati Mathematics and Statistics 2 (Arts and Science) 11th Standard Maharashtra State Board
Chapter 4 Methods of Induction and Binomial Theorem
Miscellaneous Exercise 4 | Q I. (10) | Page 85
Advertisement Remove all ads
Advertisement Remove all ads
Share
Notifications

View all notifications


      Forgot password?
View in app×