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# C2 - Tangents and normals to a circle. watch

1. Greetings, I've been baffled with a question for quite a while now and I seek help.

A circle with its centre at (2,1) has the line x+2y=9 as a tangent.

(a) Find the equation of a line through the centre, perpendicular to this tangent.

Thank you!
2. (Original post by Nightly)
Greetings, I've been baffled with a question for quite a while now and I seek help.

A circle with its centre at (2,1) has the line x+2y=9 as a tangent.

(a) Find the equation of a line through the centre, perpendicular to this tangent.

Thank you!
What is the gradient of the line ? What is the negative reciprocal of it?

Then just apply
3. (Original post by Nightly)
Greetings, I've been baffled with a question for quite a while now and I seek help.

A circle with its centre at (2,1) has the line x+2y=9 as a tangent.

(a) Find the equation of a line through the centre, perpendicular to this tangent.

The question asks you to find a line through the point perpendicular to the line . The circle is irrelevant, at least for (a).
4. (Original post by RDKGames)
What is the gradient of the line ? What is the negative reciprocal of it?

Then just apply
The gradient in this case is 1 and so the negative reciprocal is -1. When I substitute into that equation, I get y = -x +3
However, my book disagrees and says y = 2x +3 but I don't understand how.
5. (Original post by Nightly)
The gradient in this case is 1 and so the negative reciprocal is -1. When I substitute into that equation, I get y = -x +3
However, my book disagrees and says y = 2x +3 but I don't understand how.

You need to put the equation in the form y=mx+c first.

Posted from TSR Mobile
6. (Original post by RDKGames)

You need to put the equation in the form y=mx+c first.

Posted from TSR Mobile
I'm honestly ashamed I missed out on this. Thank you very much, I got the answer I needed.

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