题目

Researchers claimed that waitresses who wear red get up to 26 percent extra in tips than they would wearing other colors. However, the team finds that the sexes tip very differently—with the bigger tips coming only from male customers. No matter what color they wear, female diners will give the same kind of amounts for service every time. Yet men, whether they realize it or not, add anything between 15 and 26 percent more to a waitress in red than they would if it was the same waitress wearing a different color. The test was simple. Take 11 waitresses in five restaurants over a six-we在Rt△ABC中，，则cosB的值等于________．