If f(x) = 4x + 1 and g(x) = kx + 2 such that f o g(x) = g o f(x), then what is the value of k?  

This question was previously asked in
NDA-II 2024 (Maths) Official Paper (Held On: 01 Sept, 2024)
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  1. 7
  2. 5
  3. 4
  4. 3

Answer (Detailed Solution Below)

Option 1 : 7
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Explanation:

Given

f(x) = 4x + 1, g(x) = kx + 2

⇒ fog(x) = 4(kx + 2) + 1 = 4kx + 9

⇒ go f(x) = k(4x + 1) + 2 = 4kx + k + 2

Also fog(x) = go f(x) 

⇒ 9 = k + 2 

⇒ k = 7

∴ Option (a) is correct

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