Difference between revisions of "2005 AIME I Problems/Problem 14"

m (wikify tag -- needs links to rest of wiki)
Line 6: Line 6:
  
 
== See also ==
 
== See also ==
* [[2005 AIME I Problems/Problem 13 | Previous problem]]
+
{{AIME box|year=2005|n=I|num-b=13|num-a=15}}
* [[2005 AIME I Problems/Problem 15 | Next problem]]
 
* [[2005 AIME I Problems]]
 
  
 
[[Category:Intermediate Geometry Problems]]
 
[[Category:Intermediate Geometry Problems]]
 
{{wikify}}
 

Revision as of 12:19, 15 November 2007

Problem

Consider the points $A(0,12), B(10,9), C(8,0),$ and $D(-4,7).$ There is a unique square $S$ such that each of the four points is on a different side of $S.$ Let $K$ be the area of $S.$ Find the remainder when $10K$ is divided by 1000.

Solution

Let $(a,b)$ denote a normal vector of the side containing $A$. The lines containing the sides of the square have the form $ax+by=12b$, $ax+by=8a$, $bx-ay=10b-9a$ and $bx-ay=-4b-7a$. The lines form a square, so the distance between $C$ and the line through $A$ equals the distance between $D$ and the line through $B$, hence $8a+0b-12b=-4b-7a-10b+9a$, or $-3a=b$. We can take $a=-1$ and $b=3$. So the side of the square is $\frac{44}{\sqrt{10}}$, the area is $K=\frac{1936}{10}$, and the answer to the problem is $936$.

See also

2005 AIME I (ProblemsAnswer KeyResources)
Preceded by
Problem 13
Followed by
Problem 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
All AIME Problems and Solutions