Asked by Kaur

Consider the circles x^2+y^2=1 and x^2+y^2-2x-6y+6=0. Then find the equation of a common tangents to a circles ???
Answered by oobleck
the line joining the two centers is y=3x
the two tangents cross midway between where the line intersects the circles.
Now find where a line with slope -1/y' goes through that point.

Or, google the problem and I'm sure you will find a more general method.
Answered by Kaur
My answer is 4x-3y-5=0
Answered by oobleck
Ignore my previous post. But I don't think your equation is right either.
Consider that the two circles have
center (0,0) radius=1
center (1,3) radius=2
Then one common tangent is the line y=1
So the other will have negative slope, not a slope of 4/3
Answered by oobleck
wow - my bad. I was thinking only of the internal tangents.
Good job.
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