# 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

• -7/9

• -9/7

• 7/9

• 9/7

#### 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
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#### 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