This video will show you how to use the circle theorem that a tangent and radius make a 90 degree angle at the point of contact. A tangent is a line touching the edge of the circle and a radius is line going from the centre to the edge of the circle. If these two lines meet in the same place then they will form a right angle. So in the example given you have a triangle, where one edges of the triangle is a tangent and the other edge is the radius, and you need to find angles x and y given a 35 degree angle. X is 90 degrees as this is where a tangent meets the radius. Angle y can now be found by subtracting these angles from 180 degrees as the angles in a triangle add up to 180.

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