First of all, because any two are not parallel, the angle they form can be condensed to the same point through translation. In other words, at least one of the angles formed by five straight lines passing through the same point does not exceed 36 degrees. Suppose you record with a rotation of 36 degrees, then the last straight line will definitely exceed 36 degrees. If the math teacher insists on giving a method, you can use reduction to absurdity.