The standard form for a straight line (a linear equation) is
x and y represent points on the line. `m` is the slope or gradient and `c` is the y-intercept - that is, the point at which the line crosses the y-axis.
We have the slope (also called gradient) of a line - `l` - so we can substitute and instead of m we can replace it with `-1/3` so we can say that `l:` `y = -1/3 x+c` .We do not have any more information.
Now the rules say that the gradients of perpendicular lines, when they are multiplied, will ALWAYS equal `-1` . This has the same effect as finding the negative reciprocal of the line:
`-1/3 times m = -1` where `m` is our unknown gradient or slope
`thereforem= -1divide -1/3`
`therefore m = -1 times -3/1`
`therefore m=3` Note how the negatives cancel each other out.
So the equation of the line perpendicular to `l` is