Answer:
[tex]x=\pm \sqrt{21}/7[/tex]
Step-by-step explanation:
We can add 9 to both sides of the equation to get [tex]21x^2=9[/tex].
We can divide both sides of the equation by 21 to get [tex]x^2=9/21[/tex].
We take the square root of both sides of the equation to get [tex]x=\pm \sqrt{9/21}[/tex].
However, that isn't in the form we need.
We know that [tex]\sqrt{9/21}=\sqrt{9}/\sqrt{21}=3/\sqrt{21}=3\sqrt{21}/(\sqrt{21}*\sqrt{21})=3\sqrt{21}/21=\sqrt{21}/7[/tex]
so the answer is really [tex]x=\pm \sqrt{21}/7[/tex] and we're done!
