Hi, there-- Two angles are COMPLEMENTARY if the sum of their measures is 90 degrees. For example, a 30-degree angle and a 60-degree angle are complementary because 30+60=90. Two angles are SUPPLEMENTARY if the sum of their measures is 180 degrees. For example, a 30-degree angle and a 150-degree angle are supplementary because 30+180=90. Hope this helps! ~Mrs. Figge math.in.the.vortex@gmail.com