Final answer:
The value of x cannot be determined with the information provided. We need the coordinates of point B to use the gradient, which is the same as the slope, to find x at point C (x, -1) with a gradient of -2 for BC.
Step-by-step explanation:
To solve for the value of x at point C (x,-1) with a gradient of -2 for the line BC, you need to know the coordinates of point B. Since they are not provided, we must assume they are known or that this is part of a larger problem where B's coordinates were given or are understood from context. The gradient (or slope) formula is (y2 - y1) / (x2 - x1). If we let B be at point (x1, y1) and C be (x2, y2), which is (x, -1), the formula with the given slope -2 becomes (-1 - y1) / (x - x1) = -2. We need additional information to find the exact value of x. Without that, we cannot determine the correct answer.