Parallel and Perpendicular Lines - GCSE Maths - Steps, Examples & Worksheet The equation of a line A A is given as 5y=x−10 5y = x−10. Write the equation of a line that is parallel to A A. State/calculate the gradient of the original straight line. As 5y=x−10 5y = x − 10. Here, the gradient of the line is 1 5 51. 2 Substitute the value for m into the equation of a new straight line.