# Prove function is strictly decreasing

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• November 20th 2012, 08:08 AM
theintervurt
Prove function is strictly decreasing
I've got functions $f,g:\mathbb{R}\rightarrow \mathbb{R}$ . $f$ is strictly increasing and $f\circ g$ is strictly decreasing I am asked to show $g$ is strictly decreasing. I already have a solution in front of me however I would like to know if this approach is correct.

Suppose $x_{1} < x_{2}$ then $f\left ( g\left ( x_{1} \right ) \right ) > f\left ( g\left ( x_{2} \right ) \right )$ $\Rightarrow g\left ( x_{1} \right ) > g\left ( x_{2} \right )$ since $f$ is strictly increasing.

therefore $g$ is strictly decreasing.
• November 20th 2012, 09:51 AM
HallsofIvy
Re: Prove function is strictly decreasing
Yes, that's good.