Flag Analytical Geometry> circle and tangent...
question mark

what is the method to get equation of two tangent from a point outside the cicle to given circle???

amit agarwal , 13 Years ago
Grade
anser 1 Answers
Ashwin Muralidharan IIT Madras

Last Activity: 13 Years ago

Hi Amit,

Consider y=mx+c be the line which is a tangent.

For this to be a tangent to any circle,

Make the sub, y=mx+c in the circle equation. You will get a quad in x, which should have only one solution.

And hence the disciminant of that Quad = 0.

So you will get a relation between c and m------ (1)

Also the line should pass through a point (x1,y1). so y1 = mx1+c ---------(2) {Another relation between m and c)

So from 1 and 2, solve for m and c.

Solving between m and c, you should get a quad in m, and hence two values of m, and hence two tangents can be drawn from a point.

And hence you get the equations of the lines.

Hope that helps.

All the best,

Regards,

Ashwin (IIT Madras).

star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments