He’s not in the honors program. His papers, one teacher says, are a mess. In a school where the best and brightest are well dressed, he wears tatty running shoes, jeans, and a brightly colored T-shirt. But Rob Stringer, a high school geometry student in this upscale Boston suburb, has come up with something unknown since Euclid first discovered geometry. With the aid of a computer program developed by researchers at the nearby Massachusetts Institute of Technology (MIT) and Harvard University, he has hit upon a previously unknown geometrical theorem for dividing a triangle into smaller triangles of equal size.