问题
下列哪一项是 [锥面] 的方程？其中，$a$, $b$, $c$ 分别表示位于 $x$ 轴、$y$ 轴和 $z$ 轴上的半轴.
选项
[A]. $\frac{x^{2}}{a^{2}}$ $+$ $\frac{y^{2}}{a^{2}}$ $-$ $\frac{z^{2}}{a^{2}}$ $=$ $0$[B]. $\frac{x^{2}}{a^{2}}$ $+$ $\frac{y^{2}}{a^{2}}$ $+$ $\frac{z^{2}}{b^{2}}$ $=$ $0$
[C]. $\frac{x^{2}}{a^{2}}$ $+$ $\frac{y^{2}}{a^{2}}$ $-$ $\frac{z^{2}}{b^{2}}$ $=$ $1$
[D]. $\frac{x^{2}}{a^{2}}$ $+$ $\frac{y^{2}}{a^{2}}$ $-$ $\frac{z^{2}}{b^{2}}$ $=$ $0$
$\frac{\textcolor{orange}{x}^{2}}{\textcolor{cyan}{a}^{2}}$ $\textcolor{yellow}{+}$ $\frac{\textcolor{orange}{y}^{2}}{\textcolor{cyan}{a}^{2}}$ $\textcolor{yellow}{-}$ $\frac{\textcolor{orange}{z}^{2}}{\textcolor{cyan}{b}^{2}}$ $=$ $\textcolor{red}{0}$
