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kwal0203
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Homework Statement
Find the number of tangent lines to the curve:
[itex]y=\frac{3x}{x-2}[/itex]
which pass through the point (-1,9). Find also the points of contact of these tangent lines with the curve.
The Attempt at a Solution
1. I found the equation of lines passing through (-1,9) -> [itex]y=(x+1)m+9[/itex]
2. I thought there must be a contact point between the line through (-1,9) and the original equation so -> [itex]\frac{3x}{x-2}=(x+1)m+9[/itex]
3. I put this into a quadratic form -> [itex]mx^{2}+(6-m)x-2m-18=0[/itex]
4. I checked the discriminant of the equation in '3' -> [itex]9m^{2}+60m+36[/itex]
5. I found the roots of '4' to be [itex]x=6[/itex] and [itex]x=-\frac{2}{3}[/itex] edit: [itex]m=6[/itex] and [itex]m=-\frac{2}{3}[/itex]
I know that if the discriminant is 0 then there is one real solution. This means that there are two tangents of the original equation that also go through (-1,9).
Now I don't know how to get the equation for these two tangent lines? How can I use the roots of the discriminant to get these equations?
Any help appreciated!
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