Thread: Equations of Linear relations, perpendicular lines with a variable

The two lines -x +my +3 =0 and 2x + y +3 = 0 are perpendicular. What is the value of M?
I was away for this lesson and I don't know how to do this.
Thank you for helping me

Hiya Gideonrichter,

Perpendicularity requires that one gradient is the negative reciprocal of the other. (m = -1/m)
Rearrange the equations to get the following:

y= x/m -3/m
y= -2x -3

the gradients are: 1/m and -2,
therefore m=2