In complement, use manley_V's formula for the following triangle.

For formula E=b*h/2, replace b with side a and h will give you the length of AD.

The normal triangle that you can start calculations is for example the ADB with D=90 degrees. The corner B can be calculated as:

Sin(B)=AD/AB

Same calculate corner C.

To calculate corner A, just use A=180-B-C.

So simple! Geometry rules!