One line, 𝒚 = 3 - 4𝒙, has a negative gradient. Each positive gradient is multiplied by the negative gradient to find if any product is -1. ¼ × -4 = -1.

There are three ways a line and a circle can be associated, ie the line cuts the circle at two distinct points, the line is a tangent to the circle or the line misses the circle. To work out which ...