y=mx+c
The gradient of the perpendicular line is 3-1/2-0, or 2/2, which is 1.
the gradient therefore is -1 you have to swap the denominator and numerator then make it negative. In this case 1/1 turned upside down is still 1/1 and then you make it negative to get -1.
so y=-1x+c
To find c look at where this line would be if it had the same x coordinate as the one provided, in this case it would be (-1,1). The difference in the y axis is 2, so you need to add 2 to the second number to get (-1,3) so c=2
THis means that the equation is:
y=-1x+2