Question

Answer 1

Đặt \(\dfrac{x}{3}=\dfrac{y}{7}=\dfrac{z}{5}=k\Leftrightarrow x=3k;y=7k;z=5k\)

\(x^2-3y^2+z^2=198\\ \Leftrightarrow9k^2-147k^2+25k^2=198\\ \Leftrightarrow-113k^2=198\Leftrightarrow k^2=-\dfrac{198}{113}\Leftrightarrow k\in\varnothing\left(k^2\ge0\right)\\ \Leftrightarrow x,y,z\in\varnothing\)

Answer 2

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