Why is the stratosphere warmest at the top

Temperatures raise as the altitude increases. It also absorbs all the suns rays and energy making it warmer. 

A small research in google :

"Temperatures rise with increasing altitude in the stratosphere. Ozone molecules in the stratosphere absorb ultraviolet radiation coming from the Sun. The energy from the UV radiation is transformed into heat. The heating is most intense near the top of the stratosphere, so that is where the stratosphere is warmest."

In short, the stratosphere is warmest at the top because it absorbs UV radiation and also more the altitude is high more it's warm.

Hope this helps !

Photon

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference. 

The process by weathered rock and mineral particles are removed from one area and transported elsewhere