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AQA A-Level Maths > Coordinate Geometry > Flashcards

Flashcards in Coordinate Geometry Deck (2)
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1

How to find the equation of a tangent of a circle

Use the centre of the circle and the point where the tangent meets the circle to find the gradient of the radius.
Find the negative reciprocal of that - this is the gradient of the tangent.
Substitute the coordinates where the tangent and circle meet and the gradient of the tangent into y-y₁ = m (x-x₁)
Rearrange into the order you want

2

Federico's formula for finding the equation of a tangent of a circle

Where x₁ and y₁ are coordinates of the point where the tangent meets the circle and r is the radius of the circle:

(x*x₁) + (y*y₁) = r²