A small, rectangular park has a perimeter of 560 feet and a diagonal measurement of 400 feet. What is its area, in square feet? Choose the correct choice.
A) 76,800	B) 19,600	C) 20,000	D) 20,400	E) 20,800

Rationale: "you can avoid a lot of work in this problem by recognizing that , with the info provided , the diagonal forms a triangle inside the rectangle with sides that have a 3 : 4 : 5 ratio . diagonal = 200 2 x + 2 y = 560 , or x + y = 280 a ^ 2 + b ^ 2 = c ^ 2 for each the sides of the triangle using the ratio 3 : 4 : 5 for sides , and knowing c = 400 , you can deduce the following a = 240 b = 320 240 x 320 = 76,800 a is the answer ."
Answer: A