I came across a question which is as follows :
Is the following statements always correct ?
1) If $f'(x) > 0$ for all $x$ in the domain of the function $f(x)$ then $f(x)$ is always one-one .
My attempt to the question:
According to me the statement should always be correct since there would be no to $x$ for which the corresponding value of the function will be same . However the answer says it's false . Please explain this .
No. It is correct if the domain is an interval. But the derivative of $x\mapsto\tan x$ is positive everywhere in its domain (if the domain excludes points whose tangent is $\infty$), but the function is clearly not one-to-one. You have $\tan 0 = \tan\pi=0,$ so it's not one-to-one.