$|a|\ge\frac{\pi}{2},x=\frac{\pi}{2}\Rightarrow cosy>1$
$|x|<|a|<\frac{\pi}{2}$
$|b|\ge\pi,y=\pi\Rightarrow -1>sinx$
$|b|<\pi$
$x=0,y=b\Rightarrow cosb>0\Rightarrow |y|<|b|<\frac{\pi}{2}$
$cos|y|>sin|x|\Rightarrow |x|+|y|<\frac{\pi}{2}\Rightarrow x^2+y^2<\frac{\pi^2}{4}$
$x=\frac{a}{\sqrt{2}},y=\frac{b}{\sqrt{2}}\Rightarrow a^2+b^2<\frac{\pi^2}{2}$
我們已經盡力了 |