Question

Find an equation of the circle with center C(7,-5) which is tangent to the x-axis

Answer 1

......... well how big is the circle? ex. what's the radius

Answer 2

it does not say what the radius is

Answer 3

i know. ;)

Answer 4

thats part of the solution process to figure it out. it gives you all the clues you need to determine the radius. What defines the radius of a circle?

Answer 5

for the circle to touch the x axis, what does the radius have to be? try drawing this out. i like drawing things ^^

Answer 6

might need to know what a tangent line to a circle represents as well

Answer 7

is the radius 7 since it on the x-axis?

Answer 8

good guess; but not quite,

x axis is also the y=0 axis

what is the distance from the center y value to the xaxis y value?

Answer 9

im srry you just lost me

Answer 10

still confused

Answer 11

what is the distance from center of the circle to the x axis? this measure will define the radius for us.

Answer 12

the x axis IS y=0

the center of the circle has a y value of: y = -5

what is the distance between 0 and -5 ?

Answer 13

-5?

Answer 14

yes, but the negative part tells us a direction; its the 5 that tells us a distance. so lets define the radius as 5 units in length

Answer 15

do you recall the general formula for the equation of a circle?

Answer 16

yes it's (x-a)^2 + (y-b)^2=r^2

Answer 17

good, and the center of the circle is defined as (a,b) and we just determined r; so can you show me how you think the solution would look?

Answer 18

(x-7)^2+(y-(-5))^2=5

Answer 19

5^2

Answer 20

(a,b) = (7,-5); r=5

(x-a)^2 + (y-b)^2=r^2

(x-7)^2 + (y-(-5))^2 = 5^2

correct :)

Answer 21

also acceptable is to write (y+5)^2 for the y part

Answer 22

thxks! :)

Answer 23

good luck ;)