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geometry intermediate

Problem

When the diameter of a pizza increases by 2 inches, the area increases by . What was the area, in square inches, of the original pizza? Express your answer in terms of .
Solution
Let be the original radius of the pizza. If the diameter increases by 2 inches, then the radius increases by 1 inch. We can calculate and . Using the information given in the problem, . Substituting, we get cannot be negative, so . This means the area of the original circle is .
Final answer
25\pi