Question

Which of the function defined below is one-one?

• A. $f : \left(0, \infty\right) \to R , f \left(x\right) = x^{2} - 4x + 3$
• B. $f :[0, \infty)\to R , f \left(x\right) = x^{2} + 4x - 5$
• C. $f : R \to R , f \left(x\right) =e^{x} + \frac{1}{e^{x}}$
• D. $f : R \to R, f \left(x\right) = \ell n\left(x^{2} + x +1\right)$

Answer 1

Answer: (B)

By definition only $f (x) = x^2 + 4x - 5$ with domain $[0, \infty)$ is one to one.