a: \(A=\sqrt{16}\cdot\sqrt{25}+\sqrt{196}:\sqrt{49}\)
\(=4\cdot5+14:7\)
=20+2
=22
\(B=3\sqrt{8}-\sqrt{50}-\sqrt{\left(\sqrt{2}-1\right)^2}\)
\(=3\cdot2\sqrt{2}-5\sqrt{2}-\left|\sqrt{2}-1\right|\)
\(=\sqrt{2}-\left(\sqrt{2}-1\right)=\sqrt{2}-\sqrt{2}+1=1\)
\(C=\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{1}{x-\sqrt{x}}\right)\cdot\dfrac{1}{\sqrt{x}+1}\)
\(=\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{1}{\sqrt{x}\left(\sqrt{x}-1\right)}\right)\cdot\dfrac{1}{\sqrt{x}+1}\)
\(=\dfrac{x-1}{\sqrt{x}\left(\sqrt{x}-1\right)}\cdot\dfrac{1}{\sqrt{x}+1}\)
\(=\dfrac{x-1}{\sqrt{x}\left(x-1\right)}=\dfrac{1}{\sqrt{x}}\)
b: B=3C
=>\(1=\dfrac{3}{\sqrt{x}}\)
=>\(\sqrt{x}=3\)
=>x=9(nhận)