I can enthusiastically recommend MathType if you have to write a lot of mathematical formulas in your documents. A basic version of MathType is available in the Insert Equation part of MS Word, and is also in other Windows and Apple software programs, but I have used the full version for years to write my books.

MathType is offering their full program for 30% off, so I thought you might want to try it out. Note that MathType does not solve equations, it is merely a way to write complex math equations in a document.