答案1
你的等式
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{multline*}
\mathrm{Time} = a + b \times h_1(x) + c \times h_2(x) + d \times h_3(x) + e \times h_4(x) \\
\text{where}\ \ h_{1,2,3,4}(x) =
\begin{cases}
x & x > 0 \\
0 & x \leq 0
\end{cases}
\end{multline*}
\end{document}
强烈推荐版本
\documentclass{article}
\usepackage{amsmath}
\begin{document}
We have
\[\mathrm{Time} = a + b \times h_1(x) + c \times h_2(x) + d \times h_3(x) + e \times h_4(x)\]
where
\[h_{1,2,3,4}(x) =
\begin{cases}
x & x > 0 \\
0 & x \leq 0
\end{cases}\]
\end{document}
或者
\documentclass{article}
\usepackage{amsmath}
\begin{document}
We have
\[\mathrm{Time} = a + b \times h_1(x) + c \times h_2(x) + d \times h_3(x) + e \times h_4(x)\]
where
\[h_{1,2,3,4}(x) =
\begin{cases}
x & \text{if $x > 0$} \\
0 & \text{otherwise}
\end{cases}\]
\end{document}
答案2
这里还有另一个建议。有很多方法可以更好地编写公式。
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
\begin{flalign}
\mathrm{Time} = & \, a + b \ast h_1(x) + c \ast h_2(x) + d \ast h_3(x) + e \ast h_4(x) &\nonumber\\
\mathrm{where} & \,\ h_{1,2,3,4}(x) =
\begin{cases}
x & x > 0 \\
0 & x \leq 0
\end{cases}
\end{flalign}
\begin{flalign}
\mathrm{Time} = & \, a + b \cdot h_1(x) + c \cdot h_2(x) + d \cdot h_3(x) + e \cdot h_4(x) &\nonumber\\
\mathrm{where} & \,\ h_{1,2,3,4}(x) =
\begin{cases}
x & x > 0 \\
0 & x \leq 0
\end{cases}
\end{flalign}
\end{document}