The formula, y = mx + c, is displayed inline. Some symbols and equations (such as ∑x or $\frac{1}{2}$) are rescaled to prevent disruptions to the regular line spacing. For more voluminous equations (such as $\sum{\frac{(\mu - \bar{x})^2}{n-1}}$), some line spacing disruptions are unavoidable.
Math should then be displayed in displayed mode.
$$\sum{\frac{(\mu - \bar{x})^2}{n-1}}$$