Problem is, I don't know how to solve the equation beyond the first basic step lol

Btw, I know it can be solved with Euclide's second theorem, but I was wondering how to solve it with Pitagora, if it's possible to solve that equation I wrote. So basically I'm asking how to solve that equation.

I think that's what I was looking forward to doing, but I don't know how that would work. So, could you elaborate on the passages required? I only know about the property where you can sum/subtract, multiply/divide something left and right in an equation, but I don't know how to proceed with "squaring".

Wouldn't I get 144 = x^{2} * (25-x^{2}) from 12 = x * √(5^{2} - x^{2}) then?
It would continue as 144 = 25 x^{2} - x^{4}, which would be a grade-four equation.