Question

I'll give a medal for the first answer

Answer 1

To determine if a line is perpendicular to another line, you must take the negative reciprocal of the slope of the original line. For example, in your question, the slope of the line is 2/5. Invert this fraction and you get 5/2. Slap a negative to the front, you get a -5/2 slope of the perpendicular line.