a) \(A=\sqrt{4x+20}-2\sqrt{x+5}+\sqrt{9x+45}\)
\(=\sqrt{4\left(x+5\right)}-2\sqrt{x+5}+\sqrt{9\left(x+5\right)}\)
\(=2\sqrt{x+5}-2\sqrt{x+5}+3\sqrt{x+5}\)
\(=3\sqrt{x+5}\)
b) Để A = 6 thì \(3\sqrt{x+5}=6\Leftrightarrow\sqrt{x+5}=2\Leftrightarrow x+5=4\Leftrightarrow x=-1\) (nhận)
Vậy với x = -1 thì A = 6.
a, \(A=\sqrt{4x+20}-2\sqrt{x+5}+\sqrt{9x+45}\)
\(=\sqrt{4\left(x+5\right)}-2\sqrt{x+5}+\sqrt{9\left(x+5\right)}\)
\(=2\sqrt{x+5}-2\sqrt{x+5}+3\sqrt{x+5}\)
\(=3\sqrt{x+5}\)
b, A = 6 \(\Leftrightarrow3\sqrt{x+5}=6\) \(\Leftrightarrow\sqrt{x+5}=2\) \(\Leftrightarrow\left(\sqrt{x+5}\right)^2=2^2\)
\(\Leftrightarrow x+5=4\Leftrightarrow x=-1\)
