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C2 tangent question on circles

Hi there, there is a question
The circle C has centre (5, 2) and passes through the point (7, 3).
(c) Show that the line y = 2x 3 is a tangent to C and find the coordinates of the
point of contact.

How would you show this?
The equation of the circle i found is (x 5)^2+ (y 2)^2=5
I subbed in y = 2x 3 into the circle to get the intersection point as (3,0)
Dont know what now.. :/
Thank you for your help!
Reply 1
Original post by THESTRESS
Hi there, there is a question
The circle C has centre (5, 2) and passes through the point (7, 3).
(c) Show that the line y = 2x 3 is a tangent to C and find the coordinates of the
point of contact.

How would you show this?
The equation of the circle i found is (x 5)^2+ (y 2)^2=5
I subbed in y = 2x 3 into the circle to get the intersection point as (3,0)
Dont know what now.. :/
Thank you for your help!


You got one intersection point? (Hint)


Posted from TSR Mobile
(edited 7 years ago)
Reply 2
Original post by Kyx
You got one intersection point? (Hint)


Posted from TSR Mobile


Sorry I dont know what else that shows other than that there is 1 intersection.
Shoudnt I also do something to do with the radients to show they are the same?
Original post by THESTRESS
Sorry I dont know what else that shows other than that there is 1 intersection.
Shoudnt I also do something to do with the radients to show they are the same?


Same gradient doesn't mean they are tangent to one another. Also at C2 you would have trouble differentiating the circle.

Anyway, showing that there is only one intersection between the line and the circle is enough to show they are tangent to one another. It's pretty obvious.

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