scmetzger wrote:Please help me to explain this answer.

The top side of circular medallion made of a circular piece of colored glass is surrounded by a metal frame. If the radius of the medallion is r centimeters and the width of the metal frame is s centimeters, then in terms of s and r, what is the area of the metal frame in square centimeters?

The answer is: pi*s*(2r-s)

Thanks for your help.

Pi r^2 -(r-s)^2 which gives the desired result.

The top side of the medallion is the part outside the smaller circle. Give you metal frame the circumference of the bigger circle, that is the same as surrounding the top side- the space between the 2 circles with the a metal frame. The trap is to consider the smaller circle as having radiur r. It is the big circle that has r, so that the difference between that r and width s will give the radius of smaller circle. Hope this helps.