An equilateral triangle is inscribed in a circle, the radius is 21 inches what is the side length of the triangle to the nearest inch?

Question

The triangle is equilateral inside a corcle and the radius is 21 inches and all sides are the same length.

Answer 1

First of all, your English grammar needs help as well as your math.  A sentence ends with a period and begins with a capital letter!  You expect precision in my answer; I expect precision in your question...not to mention that you look as if you are uneducated when you use improper grammar!.

 

Draw a figure! Draw the radii to two vertices of the inscribed triangle.

 

You should see that the 2 radii make an angle of 120°.  Therefore, the side of the inscribed triangle can be obtained using the law of cosines, as follow:

 

square of the side = (21)² + (21)² - 2*21*21*cos 120°

 

I will leave the arithmetic to you.