In the diagram,
What is the total area of the red regions?
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We note that two halves of the red region at the top vertex of the pentagon fit into the bottom of the circle regions of the left and right vertices.
Therefore the area of the red region is 5 3 the area of the pentagon or A r e d = 5 3 A p e n t a g o n = 5 3 × 9 0 0 = 5 4 0 .