Question

What is the general form of the equation of a circle with a center at (11, 7) and a radius of 13?

(x – 11)2 + (y – 7)2 = 169

(x – 11)2 + (y + 7)2 = 169

(x + 11)2 + (y – 7)2 = 169

(x + 11)2 + (y + 7)2 = 169

Answer 1

i'll give the equation in "general" form, given its center (h,k) and radius r.

\[\Large (x-h)^2+(y-k)^2 = r^2\]

Answer 2

Check this
http://www.regentsprep.org/Regents/math/algtrig/ATC1/circlelesson.htm

but in general, if you replace the center (11,7) you should get 0 , 0

Answer 3

I mean replace x with 11 in the equation and y with 7 in the equation
if you get 0 for both, then 11,7 is the center

Answer 4

which one do you think is the correct answer, @brittneyy18rm ?

Answer 5

still a little confused :/

Answer 6

?

Answer 7

Here is a video that is helpful
http://www.khanacademy.org/math/trigonometry/conics_precalc/circles-tutorial-precalc/e/equation_of_a_circle_1

Answer 8

\[\Large (x-h)^2+(y-k)^2 = r^2\] is the general formula for a circle with center \((h,k)\) and radius \(r\)
in your case you have the center is \((11, 7)\) and the radius is 13
so \(h=11,k=7,r=13\)

Answer 9

(x – 11)2 + (y + 7)2 = 169 ???

Answer 10

make a direct substitution onto the formula

Answer 11

would the answer be the second choice then?

Answer 12

should be a minus sign between the y and the 7

Answer 13

the minus sign lives in the formula, so you should have
\[(x-11)^2+(y-7)^2=13^2\]

Answer 14

my bad, so it would be my first choice?

Answer 15

yup

Answer 16

I get it now :)