In geometry, the concept of a tangent to a circle is essential for understanding geometric relationships and solving various problems involving circles. The tangent to a circle at a given point is a straight line that touches the circle at exactly one point without crossing it. This tangent line is perpendicular to the radius of the circle at the point of tangency. The equation of the tangent to a circle can be derived and expressed in several forms depending on the given information.
JEE Main 2025: Sample Papers | Mock Tests | PYQs | Study Plan 100 Days
JEE Main 2025: Maths Formulas | Study Materials
JEE Main 2025: Syllabus | Preparation Guide | High Scoring Topics
Equation of the tangent to a Circle
A circle is the locus of a moving point such that its distance from a fixed point is constant.
The fixed point is called the center (O) of the circle and the constant distance is called its radius (
If the line L touches the circle, then Equation (iii) will have two equal real roots
So, Discriminant of equation (iii) = 0
In this case, the line is tangent to the circle
This is also the condition of tangency to the circle.
The equation of the tangent to a circle
Proof:
As point
Here, PT is the perpendicular to CP .
Thus,
Hence, the equation of the tangent at
now add
i.e.
(As, point
Note:
In order to find out the equation of a tangent to any 2nd-degree curve, the following points must be kept in mind:
and c will remain c.
This method is applicable only for a 2nd degree conic.
The equation of the tangent at the point
Proof:
If
put,
we get,
The equation of the tangent to a circle
Let
on
substituting this value of
which are the required equations of tangents.
Corollary: It also follows that
Point of Contact:
Solving
Thus, the coordinates of the points of contact are
NOTE:
Equation of tangent of the circle
Solved Examples Based on Equation of the tangent to a Circle:
Example 1: Let the tangent to the circle
1)
2)
3)
4)
Solution
Tangent to the circle x2 + y2 = 25 at R(3, 4) is 3x + 4y = 25
Example 2: Find the equation to the tangent of the circle
1)
2)
3)
4)
Solution
Here
So the equation of a tangent to a given circle at
Thus, we get
Hence, the answer is the option (2).
Example 3: The tangent to the circle
1) 2
2)
3) 3
4)
Solution
The equation of tangent on
It cuts off the circle
Distance of the line from the centre
Length of chord
Using concepts of intercepts
Example 4: A line meets the coordinate axes in A and B. A circle is circumscribed about the triangle OAB. If d1 and d2 are the distances of the tangent to the circle at the origin O from the points A and B respectively, then the diameter of the circle is:
1)
2)
3)
4)
Solution
Condition of tangency -
Length of perpendicular from centre of circle
is Radius of circle
- wherein
If
Equation of circum circle of triangle
Equation of tangent at origin ax + by = 0.
= diameter
Example 5: A circle of radius r such that both coordinates of its centre are positive, touches the x -axis and line
1)
2)
3)
4)
Solution
Answer (4)
Circle touches x -axis so its y -co-ordinate of
So,
h should be positive
So,
Now equation circle is
Summary
The equation of the tangent to a circle is a fundamental concept in analytic geometry that provides insights into the geometric properties and spatial relationships involving circles. Whether deriving the tangent from an external point or at a specific point on the circle, understanding these equations is essential for solving geometric problems and applying these concepts in various fields, including optimization, computer graphics, and engineering design. By mastering the methods for finding tangents, one can effectively analyze and utilize the properties of circles in both theoretical and practical applications.
19 Sep'24 09:59 PM
19 Sep'24 02:28 PM
19 Sep'24 02:27 PM
19 Sep'24 01:18 PM
19 Sep'24 12:42 PM
19 Sep'24 11:44 AM
19 Sep'24 11:43 AM
19 Sep'24 11:29 AM
19 Sep'24 11:10 AM
19 Sep'24 10:52 AM