Question

Tìm x:

a)√x^2=7

b)√x^2=8

c)√4x^2=6

d)√9x^2=|-12|

Answer 1

a) \(\sqrt{x^2}=7\)⇒\(\left(\sqrt{x^2}\right)^2=49\)⇒x=7 hoặc -7

b) \(\sqrt{x^2}=8\)⇒\(\left(\sqrt{x^2}\right)=64\)⇒x=8 hoặc -8

c) \(\sqrt{4x^2}=6\)⇒\(\left(\sqrt{\left(2x\right)^2}\right)^2=36\)⇒x=3 hoặc -3

d) \(\sqrt{9x^2}=\left|-12\right|\)⇒\(\left(\sqrt{\left(3x\right)^2}\right)^2=144\)⇒x=12 hoặc -12

Answer 2

a. \(\sqrt{x^2}=7\)

<=> \(|x|=7\)

<=> \(\left[{}\begin{matrix}x=7\\x=-7\end{matrix}\right.\)

b. \(\sqrt{x^2}=8\)

<=> \(|x|=8\)

<=> \(\left[{}\begin{matrix}x=8\\x=-8\end{matrix}\right.\)

c. \(\sqrt{4x^2}=6\)

<=> \(|2x|=6\)

<=> \(\left[{}\begin{matrix}2x=6\\2x=-6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-3\end{matrix}\right.\)