Question 1515
i must just add to this, sorry...

{{{7x^2 = 84}}}
{{{x^2 = 12}}}
x= +- {{{sqrt(12)}}}
x=+{{{sqrt(12)}}} or x=-{{{sqrt(12)}}}

Whenever you take a square root, ALWAYS remember the negative version too! It is VERY important.

As for simplifying root12....

{{{sqrt(12)}}} is {{{sqrt(4*3)}}}
{{{sqrt(4)sqrt(3)}}}
{{{2sqrt(3)}}}

jon