If radius OA has a slope of 2.5, then we can rewrite it as 5/2. Those are equal. Slope is rise over run. Our rise is 5 and our run is 2. If a line is tangent to circle O at point A, it meets point A perpendicular to the radius OA. That means that the slope of the line tangent to the circle at point A has a slope that is the opposite reciprocal. The slope of that line will be -2/5
