when should the positive-negative sign be used?

Question

anonymous · Answer

When you take the square root of a number or variable when solving an equation.

anonymous · Answer

what about when solving $$x ^{2}+(9\sqrt{3})^{2}=4x ^{2}$$ would the answer be positive-negative 9?

hero · Answer

$|x| = a$ becomes $x = \pm a$

or 

$x^2 = a$ becomes $\sqrt{x^2} = \pm \sqrt{a}$

hero · Answer

@pllfan, you can subtract $x^2$ from both sides

hero · Answer

You'll have

$(9\sqrt{3})^2 = 3x^2$

radar · Answer

When ever both the positive and negative value is to be considered.  For example measurement tolerance, error etc.   1 foot plus or minus 1 in.

hero · Answer

Then you'll have to square the left side to get:

$81 \dot\ 3 = 3x^2$

Then divide both sides by 3 to get:

$\frac{81 \dot\ 3}{3} = x^2$

hero · Answer

And that means you'll end up with $x = \pm 9$ which is what you had all along

anonymous · Answer

oh thank in other problems like $$y ^{2}=5^{2}+(5\sqrt{3})^{2} $$ would you get a positive-negative answer there too?

hero · Answer

Yes because y is squared.

anonymous · Answer

ok thank you

hero · Answer

When you see the variable you need to solve for squared, it usually means two solutions.