设A(x1,y1),B(x2,y2),满足
x1^+y1^=b^,x2^+y2^=b^,
切线PA,PB:xix+yiy=b^,i=1,2,
它们过P(acost,bsint),
∴xiacost+yibsint=b^,
∴AB的方程是xacost+ybsint=b^,
AB交x轴于M(b^/(acost),0),交y轴于N(0,b/sint),
∴S△OMN=(1/2)|OM|*|ON|=b^3/|asin2t|,
其最小值=b^3/a.
设A(x1,y1),B(x2,y2),满足
x1^+y1^=b^,x2^+y2^=b^,
切线PA,PB:xix+yiy=b^,i=1,2,
它们过P(acost,bsint),
∴xiacost+yibsint=b^,
∴AB的方程是xacost+ybsint=b^,
AB交x轴于M(b^/(acost),0),交y轴于N(0,b/sint),
∴S△OMN=(1/2)|OM|*|ON|=b^3/|asin2t|,
其最小值=b^3/a.