😀14.2 橢圓

https://www.geogebra.org/m/D55ER2yN#material/Nsd4C9yX

https://www.geogebra.org/m/D55ER2yN#material/CrVpc8pP

https://www.geogebra.org/m/rndn8y5k

https://www.geogebra.org/m/z7g8y3gm

https://www.geogebra.org/m/dywbgm6r

b^2=a^2-c^2 的幾何意義

https://www.geogebra.org/m/qjrmma4v