Straight Lines
Want to master straight line equations? You've got three main forms to work with: y = mx + c, y - b = mx−a, and Ax + By + C = 0. The gradient formula m = y2−y1/x2−x1 is your best friend here.
Parallel and perpendicular lines follow simple rules. Parallel lines have identical gradients m1=m2, whilst perpendicular lines multiply to give -1 m1×m2=−1. Here's a neat trick: to find a perpendicular gradient, flip the fraction upside down and change the sign.
To check if a point lies on a line, substitute the coordinates into your equation. If it works out correctly, the point is on the line. For points of intersection, set your equations equal and solve - this is where two lines cross.
Collinearity (three points on the same line) requires you to prove that gradients between consecutive points are equal. Don't forget to state that the lines are parallel AND share a common point.
Exam Success: Always remember that θ (the angle) is measured from the positive x-axis, and it's always on the right side of your line.