Real life example of complementary angles?

Answer 1

Complementary Goods

Goods that usually are consumed together; demand for one falls when the other's price rises; demand for one increases when the price of the other decreases. VCRs and videotapes are complementary goods; if VCRs become cheaper, people will buy more of them, and, consequently, demand for videotapes will increase.

Answer 2

A pie cut into four equal pieces. Now cut one of those four pieces into two sections anyway you like and those two pieces together will equal ninety degrees (Unless of course you ate some of the pie.)