/* Referencedesigner.com Mathjax tutorial - Subscript */ A simple equation showing usage of subscript
$$x_1 +x_2+ x_3 = 43 $$
You can use curly brackets to render subscript so length more than 1 character.

$$x_{i1}$$

You will also have to use curly bracket to render sub subscript.

$$x_{i_2}$$
Notice that x_i_2 in above will render error.

Subscripts can be combined with superscript as in

$$x_i^2$$

Aubscripts can also be applied before a literal as in

$$_bx^c$$