For an investment compounded continuously, the rule of 69 gives a better approximation than the rule of 72 (for normal compound interests).
Take out a GCF (greatest common factor, which is 3x) factor what is left, (x^2 - 4)
Please respond if you understand, or if you need more help!
63 + 36...there is a common factor of 9
9(7 + 4) <== this is equivalent
63 + 36...there is a common factor of 3
3(21 + 12)...but this is not an answer choice...but it is equivalent
we know that
the standard form of the equation of the circle is

where
(h,k) is the center of the circle
r is the radius of the circle
In this problem we have

<u>Convert to standard form</u>
Group terms that contain the same variable, and move the constant to the opposite side of the equation

Complete the square twice. Remember to balance the equation by adding the same constants to each side.


Rewrite as perfect squares


the center of the circle is 
the radius of the circle is 
therefore
<u>the answer is</u>
the radius of the circle is 