Okay, here we have this:
The error in the student's plan consists in that considering that the contrapositive of the statement "if A, then B" is "if not B, then not A.", if the student wants to prove by the contrapositive must then start by saying that if the measure of angle 1 is not less than 60 and then prove that the measure of angle 2 then it is not greater than 30. This means that he is working the operands in the wrong order.
