3d problems

I need a formula to calculate all three coordinates a third point of a triangle.

Here is a sketch of a random triangle just so it makes it easyers for me to explain my problem: TRIANGLE

I have x,y and z of points A and B, and lenght all of the sides (a,b and c)

The third point, C, must be between A and B in x-z axises (that should reduce the solutions from a circle (actualy the edge of a circle, i dont know the english term) to only 2 points), and I only need the point that is above the line c on y axis.

I could calculate that manualy, but i need a formula that works allways becouse i need it for the movement of my robot (it isnt homework, just a project =D)

Sorry for grammar mistakes, english isn't my main language, and in school we don't learn the scientifical terms...

Thank you for your help if you helped me, and if you didn't becouse you dont know how thank you for reading this, atleast you wanted to help =D