Dennis,

Look at my response to Riley's similar question. In his problem we were considering rectangles so try a circle. Suppose you have a circle of radius 2 cm. Find its perimeter (circumference) and area. Now multiply by a scale factor, for example a scale factor of 3. The circle is then expanded to one with radius 2 × 3 = 6 cm. What is its perimeter and area? How do these relate to the perimeter and area of the smaller circle?

Now try it a little more abstractly. Suppose the scale factor is k. The circle of radius 2 cm is then scaled to a circle with radius 2k cm. What is its perimeter and area? How do these relate to the perimeter and area of the original circle?

Harley