Подобие треугольников

http://www.slideboom.com/presentations/70646/%D0%9F%D0%BE%D0%B4%D0%BE%D0%B1%D0%B8%D0%B5-%D1%82%D1%80%D0%B5%D1%83%D0%B3%D0%BE%D0%BB%D1%8C%D0%BD%D0%B8%D0%BA%D0%BE%D0%B2.-%D0%A7%D0%B0%D1%81%D1%82%D1%8C-2.