Thread: Finding the radius of a circle inscribed in a sector.

Hello

I have a question where I need to find the area of a circle inscribed, I think that's the right word, in a sector. The circle touches both straight edges of the sector and the arc. I know the angle of the sector, and the lengths of the two straight edges, 6 cm. I figure I need to find the radius of the circle.

I'm just after a hint. Thank you.

think properties of 30-60-90 triangles ...

Draw the bisector of the angle and connect the circle center with the points where the circle touches the angle's sides.Then use the fact that the resulting triangles are right-angled.

Hello, Furyan!

I need to find the area of a circle inscribed in a sector.
The circle touches both straight edges of the sector and the arc.
Angle of the sector is and the lengths of the two straight edges, 6 cm.
I figure I need to find the radius of the circle. . Right!

Code:

                          B
                        * o *
                *   *     |     *   *
             *    *       |       *    *
         A o     *        |r       *     o C
            \             |             /
             \  *         |O        *  /
              \ *         o         * /
               \*         | *  r    */
                \         |   *     / 
                 *        |     *  *
               6  *       |       o
                   \*     |     */ Q
                    \   * * *   /
                     \    |    /
                      \   |   /
                       \30|30/
                        \ | /
                         \|/
                          o
                          P

We have sector

Inscribed circle: center , radius

In right triangle
. . Hence: .


Since , we have: .

Originally Posted by skeeter

think properties of 30-60-90 triangles ...

Thank you Skeeter. I hadn't spotted it was a 'special' triangle and the 2:1 connection. The graph was very helpful.

Thank you.

Originally Posted by emakarov

Draw the bisector of the angle and connect the circle center with the points where the circle touches the angle's sides.Then use the fact that the resulting triangles are right-angled.

Thank you emakarov, I had drawn the angle bisector and was wrestling with those right triangles.

Thank you.

Originally Posted by Soroban

Hello, Furyan!

Code:

                          B
                        * o *
                *   *     |     *   *
             *    *       |       *    *
         A o     *        |r       *     o C
            \             |             /
             \  *         |O        *  /
              \ *         o         * /
               \*         | *  r    */
                \         |   *     / 
                 *        |     *  *
               6  *       |       o
                   \*     |     */ Q
                    \   * * *   /
                     \    |    /
                      \   |   /
                       \30|30/
                        \ | /
                         \|/
                          o
                          P

We have sector

Inscribed circle: center , radius

In right triangle
. . Hence: .


Since , we have: .

Thank you Soroban, I have to admit that I hadn't quite got there.

, though. Right?

Thank you.