128хsin10хcos80хcos20xsin50xcos40xsin70

Умножим и разделим это выражение на сos10
(1/cos10)128sin10cos80cos20sin50cos40sin70cos10=(64/cos10)sin20cos80cos20sin50cos40sin70=(32/cos10)sin40cos80sin50cos40sin70=(16/cos10)sin80cos80sin50sin70=(8/cos10)sin160sin50sin70=(8/cos10)cos70sin50sin70=(4/cos10)sin140sin50=(4/cos10)cos50sin50=(2/cos10)sin100=(2/cos10)cos10=2