Question

Câu 1:Tìm x,y,z

a)x*y=\(\dfrac{2}{7}\); y*z= \(\dfrac{3}{2}\);z*x=\(\dfrac{3}{7}\)

b)x*y=9*z;y*z=4*x;z*x=1*by

Câu 2:Tìm x

a)\(\sqrt{x}=5\)

b)2*\(\sqrt{x}=\sqrt{12}\)

c)x²=6

d)-3\(\sqrt{x}=-\sqrt{18}\)

e)x²-1=7

f)3\(\sqrt{x^2}=\sqrt{9}\)

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Answer 1

Câu 2:

a) \(\sqrt{x}=5\)

\(\Leftrightarrow x=25\)

b) \(2\sqrt{x}=\sqrt{12}\)

\(\Leftrightarrow2\sqrt{x}=2\sqrt{3}\)

\(\Leftrightarrow\sqrt{x}=\sqrt{3}\)

\(\Leftrightarrow x=3\)

c) \(x^2=6\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\sqrt{6}\\x=-\sqrt{6}\end{matrix}\right.\)

d) \(-3\sqrt{x}=-\sqrt{18}\)

\(\Leftrightarrow-3\sqrt{x}=3\sqrt{2}\)

\(\Leftrightarrow\sqrt{x}=\sqrt{2}\)

\(\Leftrightarrow x=2\)

e) \(x^2-1=7\)

\(\Leftrightarrow x^2=8\)

\(\Leftrightarrow\left[{}\begin{matrix}x=2\sqrt{2}\\x=-2\sqrt{2}\end{matrix}\right.\)

f) \(3\sqrt{x^2}=\sqrt{9}\)

\(\Leftrightarrow3\cdot\left|x\right|=3\)

\(\Leftrightarrow\left|x\right|=1\)

\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-1\end{matrix}\right.\)

Answer 2

a, Ta có: \(\left(xyz\right)^2=\dfrac{2}{7}.\dfrac{3}{2}.\dfrac{3}{7}\)\(=\dfrac{9}{49}\)

\(\Rightarrow xyz=\sqrt{\dfrac{9}{49}}=\dfrac{3}{7}.\)

\(\Rightarrow z=\dfrac{xyz}{xy}=\dfrac{3}{7}:\dfrac{2}{7}=1,5.\)

\(\Rightarrow y=1;x=\dfrac{2}{7}\).

b, Tương tự.