How to properly write fraction in style

Question

I would like to write the following for the legend of a curve :

$$ Theta = \frac{\pi}{2}$$

Where the value $\frac{\pi}{2}$ is actually in a variable named $Theta$ (same name as the text on the lhs of the equality). Of course, I don't know in advance that $Theta=\frac{\pi}{2}$). Also, I need to add some style to my text (like making it bold, increasing its size etc), this is why I am using the function Style as below.

However, when I write this in Mathematica :

Style["Theta=" <> ToString[Theta]]

The fraction goes under the $Theta$ like in this picture :

What can I do to make Mathematica write properly what I want? I am looking for a very simple solution.

Answer 1

Don't use ToString (and especially, don't use a single argument ToString). Instead, just use expressions instead of strings:

Subscript[θ,n]==π/2

Addendum to address updated question

Again, don't use ToString. Here is how I would create your legend:

θ = Pi/2;
Style[HoldForm[θ] == θ, 20]

(Note that legends in plots are by default displayed in TraditionalForm, so that the double equal symbol gets rendered as a (long) single equal.)

Answer 2

Text["\!\(\*SubscriptBox[\(\[Theta]\), \(n\)]\)= \!\(\*FractionBox[\(\
\[Pi]\), \(2\)]\)"]

It is simplest to compose your text using the Basic Math Assistant palette.