Question 244373
Hello, 
The best way to understand this is first understand the word "Linear" It has to do with a straight line. Notice the word "line" in linear. Now the other thing to know is when using to the second power ^2 forms a curve. Parabola curve is formed. This kind of curve is like when you hold the ends of rope. The curve of the rope forms a parabola. 
OK, lot of talk but hopefully it helps you out. 
Answer is C=2pier is linear. 
RJ toftness
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