You can put this solution on YOUR website! THE PROOF IS WHEN 2 OR MORE LINES SEGMENTS WITHIN ANY TRIANGLE INTERSECT AT THE SAME POINT
DRAW A TRIANGLE ,LABEL B AT TOP OF TRIANGLE
LABEL A BOTTOM LEFT CORNER
LABEL C BOTTOM RIGHT CORNER
THEN DRAW LINES THAT INTERSECT WITHIN THE TRAINGLE AND YOU WILL
GET A BETTER UNDERSTANDING