Ответ: -1/2, sqrt(2)/2
sqrt() = кв. корень
sin(15pi/7)* sin(4pi/21) + cos(4pi/21)* cos(6pi/7) = sin(pi/7)* sin(4pi/21) - cos(4pi/21)* cos(pi/7) = -cos(4pi/21+pi/7) = -cos(pi/3) = -1/2
sin(7pi/24)*cos(pi/24) - cos(7pi/24)*sin(23pi/24) = sin(7pi/24)*cos(pi/24) - cos(7pi/24)*sin(pi/24) = sin(7pi/24 - pi/24) = sin(pi/4) = sqrt(2)/2