Don't feel bad. Some math problems are trivial, like arithmetic or differentiation. And other math problems are fundamentally difficult, like algebra or integration. If you ever meet anyone who disagrees, ask them to solve sin(x)+x=1 for x, or ask them to find the integral of x^x. Believe it or not, these simple problems have no closed form solution. The only way to solve them is to give raw numerical approximations, or to say that the problems are already in their most solved possible form.

Thr best you can do is memorize solutions for small sets of such problems, because there is no generalized strategy.