5lb Book - Page 900 #7

[cmcellini1]

Quant A
radius of circle with area of 36pie

Quant B
radius of circle with circumference 12pie

Answer C

I initially chose D.

I thought that when you take the sqaure root of something that it becomes + or - so I thought the correct answer was D, because the radius in Quant A can be -6 or +6. Is there a uniqie rule when dealing with a circle, stating the radius will never be a - number so we only use the + number after taking the square root?

Thanks for your time.
-Christina

[tommywallach]

Hey Christina,

When you take the square root of a number, there is only a POSITIVE solution.

When you take the square root of an expression containing a variable, you expect two solutions.

In other words:

Square root 36 = 6

But if x^2 = 36

and then you square root both sides,

You get x = + or - 6

I know it's weird, but it is the way the world works. : )

-t