latex源码：
\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\textbf{Newton's Law of Universal Gravitation:} $F=\frac{GMm}{r^2}$
\vskip\baselineskip
\textbf{Kepler's Laws of Planetary Motion}
\vskip\baselineskip
Here P is the time taken for a planet to complete an orbit round the sun, and a is the mean value between the maximum and minimum distances between the planet and sun. The corresponding formula in Newtonian mechanics is
\begin{align*}
\frac{P^2}{a^3}=\frac{4\pi^2}{G(M+m)}\approx\frac{4\pi^2}{GM}
\end{align*}
where M is the mass of the sun, m is the mass of the planet, and G is the gravitational constant.
\end{document}
运行效果：