The phrase "perpendicular lines intersect to form right angles" can be turned into an if-then statement by saying: If perpendicular lines intersect, then the lines form right angles. It can also be phrased as: If two lines form right angles, then the lines are perpendicular.
The original phrase is a geometric theorem that proves that if perpendicular lines intersect, right angles are formed. Alternately, lines that intersect to form right angles are perpendicular. Because of this, the if-then statement can be formed in either way and still be correct. Regardless of the other characteristics of the lines, if one of the conditions occurs, the other occurs as well.