From Förberedande kurs i matematik 1

Comments

(We only remark on a fault the first time it occurs.)

0. All displayed math formulas should be indented.
1. Don't refer to the fictitious person in the problem statement. Write a stand-alone solution.
2. Remove this full stop. The formula following the text should be part of the sentence (which means that this sentence must be rewritten).
3. In TeX you must not forget to start commands with a backslash (\), e.g. write \cos and not cos.
4. Avoid non-standard abbreviations. Moreover, it is the denominator of the right-hand side that is multiplied to both sides.

An improved solution might look like: