Prove that the angle c, which is subtended at the circumference by a semicircle is 90° or a right angle.
Draw a line, one radius long to split the triangle into two isosceles triangles as shown
Mark the angles a and b for each isosceles triangles.
Work out the other angles in each triangle
Work out the angle left at the centre. 360° – (180°–2a) – (180°–2b) = 2(a+b)
Since 2(a+b) is a straight line or 180° the angle in the semi-circle is 90°
Find the value of x: