Tg10 tg20 tg30 tg40 tg50 tg60 tg70 tg80=1
tg10*tg20*tg30*tg40*tg50*tg60*tg70*tg80=[tg10*tg80]*[tg20*tg70*][tg30*tg60] [tg40*tg50]=[tg10*ctg10]*[tg20*ctg20*][tg30*ctg30] [tg40*ctg40]=1·1·1·1=1