3.2.3

Equation of a Tangent

Test yourself

Tangent of a Circle

A circle with centre (0,0) and radius r has the equation x2 + y2 = r2. Find the tangent to the circle x2 + y2 = 25 at the point (-3,4):

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Step 1

  • First calculate the gradient of the line from the origin to (-3,4):
    • Gradient of purple line is m = 4-3
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Step 2

  • The tangent will be perpendicular to the purple line so the gradient of the tangent is -1m:
    • gradient of tangent = -1m = 34
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Step 3

  • Substitute in (-3,4) to y = 34x + c:
    • 4 = -94 + c
    • c = 254
    • So the equation of tangent is y = 34x + 254.

Jump to other topics

1Proof

2Algebra & Functions

2.1Powers & Roots

2.2Quadratic Equations

2.3Inequalities

2.4Polynomials

2.5Graphs

2.6Functions

2.7Transformation of Graphs

2.8Partial Fractions (A2 Only)

3Coordinate Geometry

4Sequences & Series

5Trigonometry

6Exponentials & Logarithms

7Differentiation

8Integration

9Numerical Methods

10Vectors

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