Difference between revisions of "Mock AIME 6 2006-2007 Problems/Problem 13"

Revision as of 02:21, 26 November 2023

Problem

Consider two circles of different sizes that do not intersect. The smaller circle has center $O$ . Label the intersection of their common external tangents $P$ . A common internal tangent intersects the common external tangents at points $A$ and $B$ . Given that the radius of the larger circle is $11$ , $PO=3$ , and $AB=20\sqrt{2}$ , what is the square of the area of triangle $PBA$ ?

Solution

$|AB|=|CD|=20\sqrt{2}$

Let $d$ be the distance between centers, and $h=|PO|=3$

$|CD|^2+(r_2-r_1)^2=d^2$

$(20\sqrt{2})^2+(r_2-r_1)^2=d^2$

$800+(r_2-r_1)^2=d^2$ [Equation 1]

By similar triangles,

$\frac{r_1}{h}=\frac{r_2}{h+d}$

solving for $d$ we have:

$d=\frac{(r_2-r_1)h}{r_1}$ [Equation 2]

Substituting [Equation 2] into [Equation 1] we have:

$800+(r_2-r_1)^2=\frac{(r_2-r_1)^2h^2}{r_1^2}$

~Tomas Diaz. orders@tomasdiaz.com

Alternate solutions are always welcome. If you have a different, elegant solution to this problem, please add it to this page.

@@ Line 22: / Line 22: @@
 solving for <math>d</math> we have:
-<math>d=\frac{(r_2-r_1)h}{r_1}</math>
+<math>d=\frac{(r_2-r_1)h}{r_1}</math> [Equation 2]
+Substituting [Equation 2] into [Equation 1] we have:
+<math>800+(r_2-r_1)^2=\frac{(r_2-r_1)^2h^2}{r_1^2}</math>

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Difference between revisions of "Mock AIME 6 2006-2007 Problems/Problem 13"

Revision as of 02:21, 26 November 2023

Problem

Solution