Question

Помоги решить пример моему другу :)

Answer 1

$frac{cos18*cos28+cos108*sin208}{sin18*sin78+sin108*sin168} = frac{cos18*cos28+cos(90+18)*sin(180+28)}{sin18*sin(90-12)+sin(90+18)*sin(180-12)} =$$frac{cos18*cos28-sin18*(-sin28)}{sin18*cos12+cos18*sin12} = frac{cos18*cos28+sin18*sin28}{sin18*cos12+cos18*sin12} = frac{cos(-10)}{sin30} = frac{cos10}{ frac{1}{2} } =$$2cos10$
Ответ: 2cos10°