# How can I write the equation in LaTeX and I need the letter t ,r is tiny?

$$\Phi s=\frac{E{\tiny t} r(S,\overline S̄ )+Etrv(S,\overline S̄ )}{|S|(9 )}$$

• You want a subscript so: E_{tr} Nov 28 '21 at 12:43
• Welcome to TeX.SE.
– Mico
Nov 28 '21 at 13:01

You should use _ to initiate subscript mode while in math mode. For sure, you need to replace \Phi s, E{\tiny t} r, and Etrv with \Phi_{s}, E_{tr}, and E_{trv}, respectively. Incidentally, \tiny is a text-mode command; don't use in math mode.

Depending on what the subscripts tr and trv mean, they should maybe be rendered in upright ("roman") rather than slanted ("italic") lettering. Both possibilities are pursued in the following code and associated screenshot.

\documentclass{article}
\usepackage{amsmath}
\usepackage{newtxtext,newtxmath} %  optional (for Times Roman text and math font)

\begin{document}
\begin{align*}
\phi_{S}(W)
&=\frac{E_{tr}(S,\bar{S})+E_{trv}(S,\bar{S})\cdot W}{|S|\cdot(3+6W)} \\[\jot]
&=\frac{E_{\mathrm{tr}}(S,\bar{S})+E_{\mathrm{trv}}(S,\bar{S})\cdot W}{|S|\cdot(3+6W)}
\end{align*}
\end{document}
• :-) there is a missing (W): to see \upphi_s(W). +1. Nov 28 '21 at 13:01
• @Sebastiano - Good catch! Let me fix that right away.
– Mico
Nov 28 '21 at 13:02

Just for fun here a possible solution:

\documentclass[a4paper,12pt]{article}
\usepackage{newtxtext,newtxmath}
\usepackage{alphabeta}

\begin{document}
$$\upphi_s(W)=\frac{ E_{\textup{tr}}(S,\overline S)+E_{\textup{trv}}(S,\overline S)\cdot W}{|S|\cdot (3+6W)},$$
\end{document}

I think, peraphs, that your \upphi is of stix font!