9A. \(2\sqrt{9y-27}-\dfrac{1}{5}\sqrt{25y-75}-\dfrac{1}{7}\sqrt{49y-147}=20\left(y\ge3\right)\)
\(\Rightarrow2\sqrt{9\left(y-3\right)}-\dfrac{1}{5}\sqrt{25\left(y-3\right)}-\dfrac{1}{7}\sqrt{49\left(y-3\right)}=20\)
\(\Rightarrow6\sqrt{y-3}-\sqrt{y-3}-\sqrt{y-3}=20\)
\(\Rightarrow4\sqrt{y-3}=20\Rightarrow\sqrt{y-3}=5\Rightarrow y=28\)
9B. \(\sqrt{4y-20}+\sqrt{y-5}-\dfrac{1}{3}\sqrt{9y-45}=4\left(y\ge5\right)\)
\(\Rightarrow\sqrt{4\left(y-5\right)}+\sqrt{y-5}-\dfrac{1}{3}\sqrt{9\left(y-5\right)}=4\)
\(\Rightarrow2\sqrt{y-5}+\sqrt{y-5}-\sqrt{y-5}=4\)
\(\Rightarrow2\sqrt{y-5}=4\Rightarrow\sqrt{y-5}=2\Rightarrow y=9\)
9A.
ĐKXĐ: $y\geq 3$
PT $\Leftrightarrow 2\sqrt{9(y-3)}-\frac{1}{5}\sqrt{25(y-3)}-\frac{1}{7}\sqrt{49(y-3)}=20$
$\Leftrightarrow 6\sqrt{y-3}-\sqrt{y-3}-\sqrt{y-3}=20$
$\Leftrightarrow 4\sqrt{y-3}=20$
$\Leftrightarrow \sqrt{y-3}=5$
$\Leftrightarrow y=28$ (thỏa mãn)
9B. ĐKXĐ: $y\geq 5$
PT $\Leftrightarrow \sqrt{4(y-5)}+\sqrt{y-5}-\frac{1}{3}\sqrt{9(y-5)}=4$
$\Leftrightarrow 2\sqrt{y-5}+\sqrt{y-5}-\sqrt{y-5}=4$
$\Leftrightarrow 2\sqrt{y-5}=4$
$\Leftrightarrow \sqrt{y-5}=2$
$\Leftrightarrow y=9$ (thỏa mãn)
