This very point has bothered me - I detest the fact that the font in my equations is so different to the rest of my doc. I explored various methods for changing font but none worked. Yesterday I stumbled across a brilliant hack for this (though not entirely fullproof).
Pages supports the /text{}
command, which can be embedded anywhere. The command is meant for including full words around equations so they don't look so odd.
How to use it within equations? Surround characters, or groups of characters with the /text{}
command. Here are some examples:
Put an overline over a character styled like the paragraph format:
\overline \text{v} \text{= ½(u+v)}
➝ v̄ = ½(u+v)
Put correctly styled characters into a fraction:
\text{t =} \frac{\text{v-u}}{\text{a}}
➝ t = (v–u) / a
Put correctly styled characters into a squareroot:
\text{F =} \sqrt{\text{134.6}} \text{= 11.6\ N}
➝ F = √134.6 = 11.6 N
Here is a visual example:

Code for top equation:
x + \frac{y}{x} = 4
Bottom equation:
\text{x} + \frac{\text{y}}{\text{z}} = \text{4}
A huge advantage of this is you select the equation object and do whatever font styling you like to the object and all the characters inside /text{} get styled accordingly. It's great. Makes it easy to add bespoke styling to different equations easily, e.g. choose a specific font, add italics, make one eqaution bold because it is a final solution to multiple steps.
Another benefit has been the ability to insert a correct degree symbol, º, which usually causes the equation editor to fail.
One main limitation that I am aware of is super and subscripts. You can style the characters inside a superscript or subscript command, e.g. \text{sin}^{\text{-1}}\text{(0.96)}
, but the characters inherit their size from the paragraph styling so they stay normal size - doesn't look right. In these cases I have resorted to either using the default font supplied in the equation editor or using Unicode (e.g. ⁻¹).
Anyway, I hope that this method adds some value to your work if you decide to try it out.