\[\theta\left(x\right)\sim\frac{\pi}{4}+\frac{2}{3}(-x)^{3/2}\left(1+\frac{5}{32%
}\frac{1}{x^{3}}+\frac{1105}{6144}\frac{1}{x^{6}}+\frac{82825}{65536}\frac{1}{%
x^{9}}+\frac{12820\;31525}{587\;20256}\frac{1}{x^{12}}+\cdots\right),\]