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C1 - Coordinate Geo - Circle / Tangents Question

Hi,

Got a question asking to find the points on the circle x^2 + y^2 - 6x -8y +15 = 0 cuts the y axis.

I know that means when x = 0.

I worked out the Centre of the circle by factorising to give C(3, 4) and the r^2 = 10

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I can work out the correct values for y when x is 0 by taking y^2 - 8y +15 = 0 and testing values individually but I am unsure of the most efficient way to find the value of y.

Is anyone able to point me in the right direction so I can speed things up a bit if I get a question like this in the exam?

Thank you
Reply 1
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Zacken
22
Original post by ghosteh

I can work out the correct values for y when x is 0 by taking y^2 - 8y +15 = 0 and testing values individually but I am unsure of the most efficient way to find the value of y.


Do you know how to solve a quadratic equation?

y2−18y+15=0y^2 - 18y + 15 = 0 is a quadratic equation in yy, factorise it to find the two solutions.
Reply 2
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ghosteh
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1
Original post by Zacken
Do you know how to solve a quadratic equation?

y2−18y+15=0y^2 - 18y + 15 = 0 is a quadratic equation in yy, factorise it to find the two solutions.


OMFG

I am going delete this thread and then kill myself. Thank you
Reply 3
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Zacken
22
Original post by ghosteh
OMFG

I am going delete this thread and then kill myself. Thank you


Hahaha, don't worry, overlooking things happens to all of us. :yes:
Reply 4
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ghosteh
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Original post by Zacken
Hahaha, don't worry, overlooking things happens to all of us. :yes:


Thanks, I've calmed down a little now. Tried to rate you a point but since you're the last person I rated it won't let me haha :smile:
Reply 5
Avatar for Zacken
Zacken
22
Original post by ghosteh
Thanks, I've calmed down a little now. Tried to rate you a point but since you're the last person I rated it won't let me haha :smile:


No problem. :smile:

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