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A=Ïd²/4
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A'=A/cosα
1ï¼ABé¢åºå
Ï(AB)=cos²(40°)*F/A
Ï(AB)=sin(40°)cos(40°)*F/A
2ï¼BCé¢åºå
Ï(BC)=cos²(50°)*F/A
Ï(BC)=sin(50°)cos(50°)*F/A
3ï¼æ大åºå
Ï(max)=F/A
Ï(max)=Ï(α=45°)=F/2A
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