... 40cos 302=+ oo22sin 80 cos 30=+ oo112cos10 cos 30=+ oooocos 30 cos102cos10 cos 30+= pooos 20 cos10 co4cos10 cos 30=o83cos 203= Baứi 19 : Cho ABC, ... Tớnho 2o 2 oPsin50 sin70cos50cos70=+ ()()()= + +ooo111P 1 cos100 1 cos140 cos120 cos20222 oTa coự : ()oo111P 1 cos100 cos140 cos 20222= + + o()oo11P 1 cos120 cos20 cos ... 2mt 2 0=+ −≤[]t1,1−∀∈ {}[,]max ( ) max ( ), ( )tgt g g∈−⇔≤ ⇔−≤110 110 {}max ), )mm⇔−−−+≤21 210 ⇔ 1m21m2−⎧≥⎪⎪⎨ ⎪≤⎪⎩m⇔− ≤ ≤1122 Bài 8 : Chứng minh 4444357A...