GRE circles and triangles rules

For circles: area = pi times r squared, circumference = 2 times pi times r. Know how to find arc length and sector area using the central angle. For triangles: area = one-half base times height, angles sum to 180 degrees. Know the Pythagorean theorem and the two special right triangles (30-60-90 and 45-45-90 ratios). These come up constantly.