I'm not sure what this lot is. ASin135 would invert the force and put it in the other direction.
Based on the image, the tension in CD is added to tension B to counteract force A.
From what I see (probably the long way around):
(((Tension in CD)Cos45)Cos[alpha]) + BCos[theta] = A
That would resolve the forces and give you equilibrium in the x plane, but I have doubts as per statement below.
However, if CD is applying a tension to the pole and forces B and A are directly opposing in the x plane, what is counteracting the y axis force exerted on the pole by the cable? Perhaps I'm overthinking it.
Please can you post the actual question, I feel something is missing.