Just a couple of comments on these.

Put a backslash before cos and sin. It will improve the spacing and remove the italics from them. Example: .

To increase the size of the parentheses around the fractions, you could write \left( and \right). So for example \left(\frac{k}{m}\right) will give . In my opinion those parentheses look too large. But you can control their size manually by the commands \bigl(, \Bigl(, \biggl( and \Biggl( (and corresponding commands like \bigr) for the closing parentheses), which give successively larger outputs. For a simple fraction, I prefer the \Big size: \Bigl(\frac{k}{m}\Bigr) will give .