Consider the points $(a,0), (0,b), (0,c)$ in the $xy$-plane, where $a,b,c>0$ and $c>b$, and $r$ is the length of the line from $(0,0)$ to $(a,c)$, and $s$ is the length of the line from $(0,0)$ to $(a,b)$. How to show that $\frac{c}{r}\geq \frac{b}{s}$
I don't see any use of similar of triangles idea, so what is the key idea here?