Because the Mission has made a problem that students have the ability to place the subject area of the triangle in either circle is delayed. And in a place must compete against time because the procedure to calculate the area of a triangle, a complex figure that is difficult and of calculated results may be made to think that there is a bias. Faculty who make approved preparation of project maths. Technique to find the area of a triangle in a circle, which this project aims to find a technique to find the area of a triangle in a circle in the way. Generally, these techniques can be used in the examination. This project carried out by the education triangle (triangle) and the type of triangle to find the triangle in the circle. Any triangle can be applied to find a formula to calculate the area of a triangle is short and fast calculations with the most accuracy. Then study circle (circle) and the trigonometric functions sine, cosine and tangent rules for a relationship between a triangle and circle, and finally it checks the validity of the area of a triangle that is available from the relationship of a triangle and a circle using the Geometer Sketchpad program. The performance showed that can be applied to find a formula to calculate the area of a triangle, shorter, and if using this recipe to make the calculations more quickly.