[tex]tga+ctga+tg3a+ctg3a= \frac{8 cos^{2}2a }{sin6a} [/tex]
доказать тождество

tga+tgb=sin(a+b)/(cosa*cosb)ctga+ctgb=sin(a+b)/(sina*sinb)sin(a+3a)/cosacos3a+sin(a+3a)/sinasin3a==sin4a(sinasin3a+cosacos3a)/sinasin3acosacos3a==4sin4acos(3a-a)/sin2asin6a==4*2sin2acos2acos2a/sin2asin6a=8cos²a/sin6a