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Let XY be a tangent to a circle, and let XA be a secant of the circle, as shown below. If AX = 15 and XY = 9, then what is AB?

 Jan 22, 2020
 #1
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Sorry, I forgot to post my diagram -

 

 Jan 22, 2020
 #2
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By power of a point, AB = 29/3.

 Jan 22, 2020
 #3
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There is a simple ratio formula fo this. I have seen Heureka use it. I've forgetton what it is though.

 Jan 22, 2020
 #4
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It is the middle one

 

In your case

 

9^2=XB * 15

81 = XB *15

XB = 81/15 = 5.4 units

 Jan 26, 2020

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