Chirkut.বাংলা

MCQ practice · SSC Higher Mathematics Board questions · Chapter 9: Exponential and Logarithmic Function

Rajshahi Board 2024

Which is the inverse function of y = log₅ x?

Think it through first, then pick an option.

  1. a y = log_x 5
  2. b y = 5ˣ
  3. c y = log_x (1/5)
  4. d y = 5⁻ˣ
Answer and explanation

Correct answer: b y = 5ˣ

If y = log₅ x then x = 5ʸ; so the inverse function is y = 5ˣ.

Why the other options are wrong

  • a y = log_x 5: In log_x 5 the base has become x; the inverse function is 5ˣ.
  • c y = log_x (1/5): log_x(1/5) is not related; the inverse is 5ˣ.
  • d y = 5⁻ˣ: 5⁻ˣ = (1/5)ˣ is the inverse of log_(1/5) x, not of log₅ x.