Answer:
2√5
Step-by-step explanation:
You were on the right track. Just move all of the numbers to one side, then take the square root of both sides. After taking the square root of both sides, you should get x = √20 , then you can simplify √20 into 2√5.
[tex]4x^{2} -31=49\\4x^{2} =80\\x^{2} =20\\x=\sqrt{20}\\x=\sqrt{4*5}\\x=2\sqrt{5}[/tex]
