When Mr. Burns is caught illegally storing excess nuclear waste, he's forced to award the town $3 mllion. Traveling salesman, Lyle Lanley (Phil Hartman) convinces the town to spend the money on a monorail.
Homer: (Wearing glasses) The sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the remaining side! Man: (From inside a bathroom stall.) That's a right triangle, you idiot! Homer: D'oh!