Tangents To A Circle
Overview
A tangent just grazes a circle, touching it at a single point. There is one beautiful fact that makes every tangent question solvable: the tangent is perpendicular to the radius drawn to the point where they touch. That right angle is the key that unlocks the equation of the tangent.
In this lesson you will use the radius-tangent right angle, together with the gradient rules you already know, to find the equation of a tangent at a given point on a circle, without any calculus. Find the gradient of the radius, take its negative reciprocal, and you have the gradient of the tangent.
Objectives
- Solve problems involving tangents to a circle, including finding the equations of tangents (no use of calculus is expected).
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Tangents To A Circle. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- A tangent to a circle is perpendicular to which line at the point of contact? A. The diameter through the centre only B. The radius at that point C. Any chord D. The x-axis Answer: B
- A circle has centre O(0,0) and passes through P(3,4). What is the gradient of the radius OP? A. 3/4 B. 4/3 C. -3/4 D. -4/3 Answer: B
- For the same circle, what is the gradient of the tangent at P(3,4)? A. 4/3 B. 3/4 C. -3/4 D. -4/3 Answer: C
- The equation of the tangent at P(3,4) to the circle centre O(0,0) is: A. y = (4/3)x B. y = -(3/4)x + 25/4 C. y = (3/4)x + 4 D. y = -(4/3)x + 8 Answer: B
- A circle has centre C(1,2) and passes through P(4,6). The tangent gradient at P is: A. 4/3 B. 3/4 C. -3/4 D. -4/3 Answer: C
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