Question

Вычислите cos⁡50°-cos⁡40°∙ctg⁡115°

Answer 1

cos50 - cos40*ctg115
= cos50 - cos(90 - 50)*ctg(90 + 25) =
= cos50 + sin50*tg25 =
= cos50 +(sin50*sin25)/ cos25 =
 = (cos50cos25 + sin50*sin25)/ cos25 =
= cos(50-25)/cos25 =
 = cos25/cos25 = 1