The answer should be half (root number 5-1). Because many mathematical symbols can't be entered here, I'll tell you the train of thought. We use substitution to eliminate elements. First, express C with the relationship of X, A and B, so C = XB-(X- 1)A, then X (B-A) = You will find that the square of (B-A) can be rounded, and finally x = 1-X, then use the bulbous formula, and because of 0 "X".