1)Ctg11°+ctg34°; 2) tg85°+ctg85° 3) ctg50°-ctg20° 4) tg15°+ctg75° 5) ctg15°-tg75° преобразовать в произведение; хотя

Используем формулы:CtgA = cosA/sinA,Tg A = sinA/cos A,sinA*cosB + sinB*cosA = Sin(A+B),Cos^2 A + sin^2 A = 1,sinA*cosB – cosA*sinB = sin(A-B).cosA*cosB – sinA*sinB = cos(A+B).1)Ctg11°+ctg34° = cos11/sin11 + cos34/sin34 = (cos11*sin34 + cos34*sin11)/(sin11*sin34) = sin(11 + 34)/(sin11*sin34) = sin45/(sin11*sin34) = √2/(2*sin11*sin34).2) tg85°+ctg85° = sin85/cos85 + cos85/sin85 = (sin^2 (85) + cos ^2 (85))/(cos85*sin85) = 1/(cos85*sin85).3) ctg50°-ctg20° = cos50/sin50 – cos20/sin20 = (cos50*sin20 – sin50*cos20)/(sin50*sin20) = sin(-30)/(sin50*sin20) = -sin(30)/(sin50*sin20) = -1//2*sin50*cos20).4) ctg15°-tg75° = cos15/sin15 – sin75/cos75 = (cos15*cos75 – sin75*sin15)/(sin15*cos75) = ccs(15+75)/(sin15*cos75) = cos90/(sin15*cos75) = 0.