证明题39(a)不会做,

1个回答

BE = BDcosθ = 1*cosθ = cosθ
AB = 2BE = 2cosθ
OB = ABcosθ = 2cos²θ
OA = ABsinθ = 2cosθsinθ
S = (1/2)OA*OB = 2sinθcos³θ