Đáp án:
1
Giải thích các bước giải:
$\dfrac{x}{a}+\dfrac{y}{b}+\dfrac{z}{c}=1\\
\rightarrow (\dfrac{x}{a}+\dfrac{y}{b}+\dfrac{z}{c})^2=1\\
\rightarrow \dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}+\dfrac{z^2}{c^2}+2(\dfrac{x}{a}\dfrac{y}{b}+\dfrac{y}{b}\dfrac{z}{c}+\dfrac{z}{c}\dfrac{x}{a})=1\\
\rightarrow \dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}+\dfrac{z^2}{c^2}+2\dfrac{x}{a}\dfrac{y}{b}\dfrac{z}{c}.(\dfrac{a}{x}+\dfrac{b}{y}+\dfrac{c}{z})=1\\
\rightarrow \dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}+\dfrac{z^2}{c^2}=1$
