Illuminations: Half Angle

Half Angle


If you want to inscribe a circle within a triangle, where will the center of the circle lie? This applet allows you to find the incenter of a triangle, as well an a visual explanation of why it occurs where it does.

Instructions

 
The Show/Hide buttons can be used to show the angle bisectors as well as a circle with its center at the intersection of the angle bisectors.

Drag the indicated point on the circle until the circle is tangent to all three sides of the triangle.

Exploration

 
A circle inscribed in a circle is known as an incircle. The center of this circle is known as the incenter of the triangle.
  • Where does the incenter occur?

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NCTM Resources

Principles and Standards for School Mathematics

Lessons


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