Complement

Complement of an angle, in Geometry, is that angle which must be added to the first to make up 90°. Thus the complement of 15° is 75°, and of 100° is -10°. So, also, in Astronomy the complement of the altitude of a heavenly body is its zenith-distance. In Arithmetic, two numbers are complementary, which, when added together, give the next higher power of ten than the greater of the two numbers. Thus, 65-1/2 and 34-1/2 are complementary, their sum being 100. In Music, complementary intervals are those which make up an octave. In Optics (q.v.), complementary colours are those which combine to form white light, such as red and green.