markdown与数学公式

\[test \]

\(test\)

\[b = \begin{cases} b_1, & \text{if}\ b_1 > 0 \\ b_2, & \text{if}\ b_2 > 0 \\ \frac{b_1 + b_2}{2} & \text{otherwise} \end{cases} \]

test

\[b = \begin{cases} b_1, & \text{if}\ b_1 > 0 \\\\ b_2, & \text{if}\ b_2 > 0 \\\\ \frac{b_1 + b_2}{2} & \text{otherwise} \end{cases} \]