Question

for what values of a is the line y=ax a tangent to the circle x^2+y^2+20x-10y+100=0

Answer 1

well you have to do the following:
1)equalize the y's with each other ,of course you get y in the circle by completing the square and solving for it,
2) differentiate the equation of the circle and set y prime equals to a
so you will be having 2 relations to solve for the points..