Circumscribed circle of a triangle, step by step
Draw a circle through all three corners of a right triangle and something surprising happens.
The question
cm
The circle through a 27-36-45 triangle's corners
right angle on the circle→180° at the center
the 45 cm side=the diameter
45 ÷ 2=22.5
- The corner between the two short sides is a RIGHT angle, and it is sitting on the circle looking straight across at the hypotenuse. An angle on a circle is half the one at the center, so the angle at the center here is 180° — a straight line.
- A straight line through the center IS a diameter. So the hypotenuse is the diameter, and the center of the circle is its midpoint — not somewhere inside the triangle.
- The radius is half the diameter: 45 ÷ 2 = 22.5. So the circle through all three corners has a radius of 22.5 cm, and the two short sides never come into it.
How it works.
- 01
The corner between the two short sides is a RIGHT angle, and it is sitting on the circle looking straight across at the hypotenuse. An angle on a circle is half the one at the center, so the angle at the center here is 180° — a straight line.
- 02
A straight line through the center IS a diameter. So the hypotenuse is the diameter, and the center of the circle is its midpoint — not somewhere inside the triangle.
- 03
The radius is half the diameter: 45 ÷ 2 = 22.5. So the circle through all three corners has a radius of 22.5 cm, and the two short sides never come into it.