document.write( "Question 294471: explain why radius squared divided by y1 is the y-intercept in the equation of the line tangent to the circle x^2+y^2=r^2\r
\n" ); document.write( "\n" ); document.write( "like in this example: x^2+y^2=17 and the circle meets the tangent at (1,4).What is the equation of the tangent line. The answer is y=(-1/4)x+(17/4)\r
\n" ); document.write( "\n" ); document.write( "Why does the (17/4) equal the radius squard by y1? \n" ); document.write( "
Algebra.Com's Answer #212358 by Edwin McCravy(20060)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "AB is tangent to circle O, whose equation is \"x%5E2%2By%5E2=r%5E2\".\r\n" );
document.write( "OT is a radius (of length r) drawn to T(x1,y1),\r\n" );
document.write( "the point of tangency. Therefore OT is perpendicular to AB.\r\n" );
document.write( "OB has length b, the y-coordinate of the y-intercept of AB and \r\n" );
document.write( "B is the point (0,b).  \r\n" );
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document.write( "All triangles in the figure above are right triangles, and\r\n" );
document.write( "all of them are similar!  This is easy to see if you\r\n" );
document.write( "realize that the pair of acute angles in each of them are\r\n" );
document.write( "equal in measure.  In particular since triangles OTB and TDO\r\n" );
document.write( "are similar,  \r\n" );
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document.write( "\"%28OB%29%2F%28OT%29=%28OT%29%2F%28TD%29\"\r\n" );
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document.write( "Observing their lengths:\r\n" );
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document.write( "\"b%2Fr=r%2Fy%5B1%5D\"\r\n" );
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document.write( "\"b=r%5E2%2Fy%5B1%5D\"\r\n" );
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document.write( "Edwin
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