How do I find the diameter of (x + 4)^2 + (y – 9)^2 = 18?

Question

phi · Answer

the equation for a circle with a center at (h,k) and with radius r is
$$ (x-h)^2 + (y-k)^2 = r^2 $$

match that to your equation.  what is r^2 in your equation?  what is r in your equation
then remember the diameter is 2 times the radius.  i.e. d= 2r

anonymous · Answer

Which is h and which is k? @phi

phi · Answer

the h goes with the x  and the k goes with the y.  But in this case, all you care about is 
"what is r^2" ?

anonymous · Answer

r^2 refers to the radius. Isn't it 6√2 or 8.485?

anonymous · Answer

Wait no.. √18 or 3√2

phi · Answer

r^2 is 18  (one step at a time)

r is the square root of 18
$$ r= \sqrt{18} = \sqrt{2\cdot 9} = \sqrt{9} \cdot \sqrt{2} = 3\sqrt{2} $$

last step, the diameter is 2 times the radius

anonymous · Answer

Right, got it. So 3√2*2=6√2.

phi · Answer

yes, 6√2 is the diameter of your circle.

anonymous · Answer

Okay, thank you so much! I really appreciate it. c:

phi · Answer

yw