← CBSE Class 10 (age 15) Mathematics ยท Circles

Theorem: Tangent Perpendicular to Radius

Practice Quiz

Q1. What is the angle between a tangent and the radius at the point of contact?

โœ” The theorem states the tangent is perpendicular to the radius, meaning the angle is exactly ninety degrees.

Q2. If radius is 3 cm and tangent is 4 cm, what is the distance from center to external point?

โœ” Using Pythagoras theorem, the square root of nine plus sixteen equals five centimeters.

Q3. How many tangents can be drawn from a single point on the circle?

โœ” From any point on the circumference, exactly one tangent line can be drawn perpendicular to the radius.
Show transcript
[Slide 1] Visualizing the Tangent
Think of a wheel touching the ground. The line from center to touch point is perpendicular. This prevents the wheel from sliding sideways.

[Slide 2] The Tangent Radius Theorem
This theorem states the tangent line is perpendicular to the radius. It happens exactly at the point of contact. Always remember this creates a right angle.

[Slide 3] Solving a Real Problem
Let us solve a problem with real numbers. The radius is three centimeters and tangent is four. We must find the distance from center to point P.

[Slide 4] Applying Pythagoras Theorem
Since we have a right angled triangle, use Pythagoras theorem. Add the squares of radius and tangent lengths. The square root of twenty-five is five.

[Slide 5] Avoiding Common Errors
Students often forget to mark the right angle. Sometimes they mistake the tangent for the hypotenuse. Remember the line from center is always hypotenuse.

[Slide 6] Key Takeaways Summary
Remember the tangent touches at only one point. The radius is always perpendicular to this line. This helps solve many geometry problems easily.