Question

what is the equation of a circle whose center is (-5,3) and passes through the point (-1,3)?

Answer 1

circle formula: (x - h)^2 + (y - k)^2 = r^2 when center is (h, k)
and radius (r) is the distance between (-5, 3) and (-1, 3)

Answer 2

this is a really dumb question but do we have a radius yet?

Answer 3

what do you mean "do we have a radius yet?" you can get the radius by finding the distance between (-5, 3) and (-1, 3)

Answer 4

oh okay sorry

Answer 5

it's alright :) then once you have all your values, you can plug it into the circle formula ^.^

Answer 6

thank you:)) I just honestly have no idea what im doing here!!

Answer 7

then once you think you've got your formula could you post it so I could help check it over for you? :)

Answer 8

wait- so I got that the radius was the square root of 16,but now what numbers do I plug into the circle formula?

Answer 9

circle formula: (x - h)^2 + (y - k)^2 = r^2 when center is (h, k)
so the center you have is (-5, 3)
so (x-(-5))^2+(y-(3))^2=(√16)^2
which can be simplified

Answer 10

ohhh!okay so I got (x+5)^2+(y-3)^2=16

Answer 11

yep :)

Answer 12

thank you!! would you mind if you checked out another one?(:

Answer 13

sure :)

Answer 14

thanks!

Answer 15

what are the coordinates of the center of a circle if the endpoints of its diameter are A(8,-4) and B(-3,2)?

Answer 16

find the midpoint of (8, -4) and (-3, 2)

Answer 17

I got M=(2.5,-1)

Answer 18

yup :) so that's the center of the circle :D

Answer 19

finally! geometry is so confusing

Answer 20

:p

Answer 21

lol your welcome :)

Answer 22

can I send you another one because I just realized I don't know how to do this whole worksheet???!

Answer 23

lol sure :)

Answer 24

which set of equations represents two circles that have the same center?
1)x^2+(y+4)^2=16 and (+4)^2+y^2=16
2)x-7^2+y-2^2=16 and x+7^2+y+^2=25
3)x-2^2+y-5^2=16 and x-2^2=y-5^2=25

Answer 25

well knowing that circle formula: (x - h)^2 + (y - k)^2 = r^2 when center is (h, k)
what values match? ^ ^

Answer 26

1 ?

Answer 27

no because x^2+(y+4)^2=16 and (x+4)^2+y^2=16
^ and ^ don't match ^ and ^

Answer 28

2? but they don't have the same radius

Answer 29

wait 3 actually

Answer 30

3 is correct :) because it was just asking for same center, not same radius

Answer 31

ohhhh okay thank you! only one more!

Answer 32

a circle has the equation (x-3)^2+(y+4)^2=10. find the coordinates of the center of the circle and the length of its radius

Answer 33

well knowing that circle formula: (x - h)^2 + (y - k)^2 = r^2 when center is (h, k)
center would be ^ ^
and radius would be ^

Answer 34

center would be (-3,4) and radius would be the square root of 10?

Answer 35

ah, that's where most people get it wrong
see, in the equation (x - h)^2 + (y - k)^2 = r^2 when center is (h, k)
see how that is a negative h? and a negative k?
so it's more like (x + (-h))^2 + (y + (-k))^2 = r^2
so in (x-3)^2+(y+4)^2=10 think of it as
(x+(-3))^2 +(y+(4))^2=10
so your center would be (3, -4)

Answer 36

ughhh I was thinking that too but I wasn't sure- so you basically just have to do it backwards- like find out the original problem?

Answer 37

yep :)

Answer 38

thank you so much!! math is not my strong point as you can probably see lol

Answer 39

it's fine :) I glad I can help people out :P
i gtg good night ^.^

Answer 40

:)) goodnight!