In a triangle there are three points in each corner, S, T, O, Point S has At an angle of 40°, the point T is a point of tangency, so what would be the angle of point O?
Since point T is a point of tangency, it lies on the straight line tangent to the circle at point O. This means that angle SOT is a right angle, or 90°.
Since angle SOT is already 40°, angle OST would be the remaining 50° to make a total of 90°.
Therefore, the angle of point O would be 50°.