Determine the equation of the straight line that passes through 0 and which is perpendicular to the line with the equation, y = 2x. Solution
The line y=2x has a gradient 2.

Therefore, the required line has a gradient -1/2

(Using the fact that the product of the gradients of perpendicular lines = - 1)

The equation of the
the required line
line is

(y-0)/(x-0) = -1/2. 2y= -x

Someone please explain-

Therefore, the required line y = 2x has gradient -1/2

How did it reach to this conclusion?​