2. In the triangle ABD you have:
3. In the right triangle left of A you have:
4. Now use similar right triangles:
which yields: ..........
5. Combine  and  and you have to solve for x:
6. After moving some stuff around you'll get:
7. You can show that x = -2 must be a solution of the equation, that means you can factor the LHS:
8. Therefore the only possible solution is