Anyone good at maths

How do I work this out?
Q: Write down the gradient of a line that is perpendicular to the line y=4x.

Is it something to do with reciprocals? ahhh I really can't remember how to do it!

thanks.

A line that is parallel will have the same gradient. A line that is perpendicular will have a gradient that that intersects the line at 90 degrees. A quick way to tell if two lines are perpendicular is to multiply their gradients together to get -1.

So the line you have is y = 4x. The line that is perpendicular is y = mx such that 4m = -1.

Rearranging 4m=-1 gives us m = -1/4.

Hence the line y = (-1/4)x will be perpendicular to y = 4x.

http://www.bbc.co.uk/schools/gcsebitesiz…
hope this helps.