matplotlib自带mathtex引擎，不需要安装TeX系统
$作为开始和结束符，如'$ y = x**2 $' 

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_xlim([1, 7])
ax.set_ylim([1, 5])

ax.text(2, 4, r"$\alpha_i \beta_j \pi \lambda \omega $", size = 15)
ax.text(4, 4, r"$ \sin(0) = \cos(\frac{\pi}{2}) $", size = 15)
ax.text(2, 2, r"$ \lim_{x \rightarrow y} \frac{1}{x^3}$", size = 15)
ax.text(4, 2, r"$ \sqrt[4]{x} = \sqrt[2]{y} $", size = 15)
plt.show()