1988 AJHSME #9
Source:
June 21, 2011
Problem Statement
An isosceles triangle is a triangle with two sides of equal length. How many of the five triangles on the square grid below are isosceles? [asy]
for(int a=0; a<12; ++a)
{
draw((a,0)--(a,6));
}
for(int b=0; b<7; ++b)
{
draw((0,b)--(11,b));
}
draw((0,6)--(2,6)--(1,4)--cycle,linewidth(1));
draw((3,4)--(3,6)--(5,4)--cycle,linewidth(1));
draw((0,1)--(3,2)--(6,1)--cycle,linewidth(1));
draw((7,4)--(6,6)--(9,4)--cycle,linewidth(1));
draw((8,1)--(9,3)--(10,0)--cycle,linewidth(1));[/asy]