2sin180+tg10*tg70*tg20*tg80

2sin180 = 2*0 = 0
tg10*tg80 = ctg80*tg80 = 1
tg70*tg20 = ctg20*tg20 = 1
- > 2sin180 + tg10*tg70*tg20*tg80 = 1*1 = 1
т.к.  sin(90 - α) = sin90*cosα - cos90*sinα = cosα
      cos(90 - α) = cos90*cosα + sin90*sinα = sinα