Point of contact of circle an tangent

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SUMMARY

The discussion focuses on determining the coordinates of the point of contact of a tangent to a circle from an external point, given the circle's center and radius. The method involves drawing a line from the external point to the circle's center, finding the midpoint, and constructing a circle using this line as the diameter. The intersection points of this circle with the original circle yield the tangent points. The mathematical equations involved include the line equation y=mx+k and the circle equation (x-a)^2+(y-b)^2=r^2, which can be solved simultaneously to find the tangent points in terms of the constants m, k, a, b, and r.

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sachin patil
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I want to find out the co-ordinate of point of contact of tangent to a circle from external point when its center and radius are known. Please Help me . . .
Thank you in advance . . .
 
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upload_2015-3-17_12-9-34.png
This figure illustrates what you need to get ahead. The tangent and the radius to the tangent point meet at 90°. Thus: Draw a line from the given point to the center of the circle, find the midpoint and draw a circle with the line as diameter. The point where this circle intersects the given circle is the tangent point (as you can see from the figure, there are two tangent points).
 
What happens when you simultaneously solve

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

For x and y? They'll be in terms of the m,k,a,b,r constants, but it can be done.
 

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