# Thread: if the planes are perpendicular, what is k?

1. ## if the planes are perpendicular, what is k?

Determine value of k when thehse are perpendicular:
[x,y,z] = [1+4s+kt, 2+2s+t, 7+2t]
and
[x,y,z] = [4,1,-1] + s[1,0,5] + t[0,-3,3]

I learned that in 2 and 3D, two lines are perpendicular only if, after solving for the t in front of the direction vector, x=x , y=y and z=z
My attempt was to Cross product the direction vecotrs in each of the equations, and then dot product those values to find k, since if they are perpend. then dot product=0
I'm not sure how they ended up with k = 31/3

2. Originally Posted by TN17
Determine value of k when thehse are perpendicular:
[x,y,z] = [1+4s+kt, 2+2s+t, 7+2t]
and
[x,y,z] = [4,1,-1] + s[1,0,5] + t[0,-3,3]

I learned that in 2 and 3D, two lines are perpendicular only if, after solving for the t in front of the direction vector, x=x , y=y and z=z
My attempt was to Cross product the direction vecotrs in each of the equations, and then dot product those values to find k, since if they are perpend. then dot product=0
I'm not sure how they ended up with k = 31/3
I'm pretty sure that this is a typo. I've got k = -12.