A base of a pyramid is a square of side 10. The lengths of three consecutive side edges are 8, 6, 10. Calculate the lenght of the fourth side edge.
I have not the slightest idea how to touch this. The triangle sides aren't isosceles so the line $|OO'|$ where $O$ is the apex and $O'$ is the point of the base diagonals crossing is not perpendicular to the base. Therefore, I simply don't know how to move on with this.. I see no angles to use some trigonometry on, nor any friendly right triangles which I could use to calculate something. Could you please help?