# Friedmann

$$
H^2 = \left({\dot{a} \over a}\right)^2 ={8 \pi G \over 3}\rho -{kc^2 \over a^2}+{\Lambda c^2 \over 3}
$$

# 1~100加總

$$
\sum_{i=1}^{100} i=1+2+3+....+99+100 = 5050
$$