Earthquakes release seismic waves that occur in concentric circles from the epicenter of the earthquake. Suppose a seismograph station determines the epicenter of an earthquake is located 9 kilometers from the station. If the epicenter is located at the origin, write the equation for the circular wave that passes through the station.

Question

anonymous · Answer

if the center of the circle is at the origin

and the station is 9 kilometers from the center

that means that the radius is 9

and you should easily be able to determine the equation of a circle with the given informaion

anonymous · Answer

A    x2 + y2 = 81

    B   x2 + y2 = 9

   C      (x - 9)2 + (y - 9)2 = 0

   D    (x + 9)2 + (y + 9)2 = 0

anonymous · Answer

you already know (from the previous question) that the equation of a circle is
$$(x - h)^{2} = (y - k)^{2} = r^{2}$$

it said that the center is at the origin (If the epicenter is located at the origin...) so (h, k) = (0, 0).

since the station is 9 km away, the radius (r) will be 9. plug in those values and you should have it.

anonymous · Answer

I do online school so its really hard :( to learn math on my own and i have 17 days left to finish everything

anonymous · Answer

the previous question has nothing to do with this question

anonymous · Answer

circle equation
$$(x-x_0)^2+(y-y_0)^2=r^2$$

where
(xo,yo) is the location of the center of the circle
and r is the radius

anonymous · Answer

So A?

anonymous · Answer

i already gave you everything you need to solve the problem

so have more confidence in your own abilities

anonymous · Answer

but yes its right

anonymous · Answer

Right the radius is 9 so 9 squared is 81?

anonymous · Answer

okay thank you soooo much :DD