A perpendicular line would have a slope that is the negative reciprocal of the slope you are given. Therefore the slope of the new line would be -4/1 or just -4. You can now use point-slope formula and plug in your numbers to figure out the equation of that line. Point-Slope form: y-y1=m(x-x1) Therefore your equation would be: y-5=-4(x-5)
