De thi HSG Ca Si O
De Thi HSG ca sio Huyên
... 2α ;
·
ADB
= 45
o
+ α
Ta có :
AH = ABcosα = acosα = 2,75cos37
o
25’ = 2,184154248 ≈ 2,18 (cm)
o
o
os 2,75 os37 25'
2,203425437 2,20( )
sin(45 ) sin(45 ) sin82 25'
o o
AH ac c
AD cm
α
α ... HD = AH.cotg(45
o
+ α)
Vậy :
( )
2 2 o
1
os cotg2 cotg(45 + )
2
ADM
S a c
α α α
= −
( )
2 2 o o
1
2,75 os 37 25' cotg74 50' cotg82 25'
2
o
ADM
S c= −
= 0,32901612...