JEE MainMathematicsBinomial Theorem
The remainder when 13^ 14¹⁵ is divided by 11 is :
Options
- A1
- B2
- C9
- D5
Correct answer
D. 5
Step-by-step solution
We need to find the remainder when 13^ 14¹⁵ is divided by 11 . First, reduce the base modulo 11 : 13 2 11 So, we need to find 2^ 14¹⁵ 11 . By Fermat's Little Theorem, a^ p-1 1 p for a prime p . Here p = 11 , so: 2¹⁰ 1 11 This means we need to find the remainder of the exponent 14¹⁵ when divided by 10 . Let x = 14¹⁵ 10 . Since 14 4 10 , we have x 4¹⁵ 10 . Let us observe the powers of 4 modulo 10 : 4^1 4 10 4^2 = 16 6 10 4^3 = 64 4 10 4^4 = 256 6 10 The sequence of remainders is 4, 6, 4, 6, For any odd power, 4^ odd