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Mathematics 16 Online
OpenStudy (anonymous):

the equation of a circle is (x-6)sq +(y+3)sq=36.THe point (8,-3) is on the circle. What is the equation of the line that is tangent to the circle at (8,-3)?

ganeshie8 (ganeshie8):

whats the center of given circle ?

OpenStudy (anonymous):

this is all it tells me :(

OpenStudy (anonymous):

I got 4 answers to pick from 1- y=8 2- x=8 3- x=-4 y=4

ganeshie8 (ganeshie8):

you can tell the `center` of the given circle from its equation

OpenStudy (anonymous):

I have to take this final exam in 3 hours

ganeshie8 (ganeshie8):

\[\large (x-6)^2 +(y+3)^2=36 \] \[\large (x-6)^2 +(y-(-3))^2=6^2\]

ganeshie8 (ganeshie8):

compare ot wid the standard form of circle : \[\large (x-h)^2 + (y-k)^2 = r^2\] center = \((h, k)\) radius = \(r\)

OpenStudy (anonymous):

ok was not sure how to do that part but know I do lol

ganeshie8 (ganeshie8):

compare them and tell me what the center is

ganeshie8 (ganeshie8):

can you ? :)

OpenStudy (anonymous):

would it be 3

ganeshie8 (ganeshie8):

center of a circle is a POINT, its not some number okay ?

ganeshie8 (ganeshie8):

a POINT can be represented using x and y value : (a, b)

OpenStudy (anonymous):

I think its time for bed I am so frustrated :(

ganeshie8 (ganeshie8):

\[\large (x-6)^2 +(y-(-3))^2=6^2\] \[\large (x-h)^2 + (y-k)^2 = r^2\]

ganeshie8 (ganeshie8):

just compare above two equations and see if u can tell me below : \(h = ?\) \(k = ? \)

ganeshie8 (ganeshie8):

this is easy, the only tricky part is finding the center

ganeshie8 (ganeshie8):

and finding the center is easy once u know how to find it

ganeshie8 (ganeshie8):

by comparing both the equation I get : \(\large h = 6\) \(\large k= -3\) so, center of circle = \(\large (6, -3)\)

OpenStudy (anonymous):

I got that part but did not know it was the center

ganeshie8 (ganeshie8):

|dw:1405592942167:dw|

ganeshie8 (ganeshie8):

Notice that both `center` and the `given point` have same y value : -3 that means slope = 0

OpenStudy (anonymous):

yes

OpenStudy (anonymous):

but I get 2 on the other

ganeshie8 (ganeshie8):

|dw:1405593076978:dw|

ganeshie8 (ganeshie8):

|dw:1405593132262:dw|

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