x/acosθ+y/bsinθ=1
x^2/a^2cosθ^2+y^2/b^2sinθ^2+2xy/absinθcosθ=1
x/asinθ-y/bcosθ=1
x^2/a^2sinθ^2+y^2/b^2cosθ^2-2xy/absinθcosθ=1
两式相加:
x^2/a^2+y^2/b^2=2.
x/acosθ+y/bsinθ=1
x^2/a^2cosθ^2+y^2/b^2sinθ^2+2xy/absinθcosθ=1
x/asinθ-y/bcosθ=1
x^2/a^2sinθ^2+y^2/b^2cosθ^2-2xy/absinθcosθ=1
两式相加:
x^2/a^2+y^2/b^2=2.