If I have a function and another point that does not lie on the function, how would I find points on the graph, that if connected with the other point, create a tangent line?

Question

joachim · Answer

concrete example: $$f(x)=1/(x+2)$$ and P(4;-1)
find the two points on the graph f which are such that the line joining these points to P are tangent to the graph.

anonymous · Answer

nice question..

anonymous · Answer

|dw:1334038103265:dw|
take the derivative of f(x) and set it equal to (b- -1)/(4 - a)
i guess we have to locate (a, b)