angle of c should have been in the opposite direction.

As a side note, you gave vectors

a b (45 deg @ 30m)
a c (20 deg @ 35m)

You are asking for b c (sloping down to right)

Hence:
a b + b c = a c
or
b c = a c - a b

That is why I suggested Subtraction.

--
Dana DeLouis

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