# Thread: Determine whether the planes are perpendicular

1. ## Determine whether the planes are perpendicular

I know how to tell when the planes are parallel, but not perpendicular, if anyone could help out.

Determine whether the planes are perpendicular:

3x - y + z - 4 = 0;
x + 2z = -1

Another one,

Determine whether the line and plane are perpendicular:

x = -2 -4t
y = 3 - 2t
z = 1 + 2t
2x + y - z = 5

Any help is greatly appreciated!

2. Originally Posted by DarK
I know how to tell when the planes are parallel, but not perpendicular, if anyone could help out.

Determine whether the planes are perpendicular:

3x - y + z - 4 = 0;
x + 2z = -1

Another one,

Determine whether the line and plane are perpendicular:

x = -2 -4t
y = 3 - 2t
z = 1 + 2t
2x + y - z = 5

Any help is greatly appreciated!
Two planes are perpendicular if the scalar product of their normals is equal to zero.

A line and a plane are perpendicular if the scalar product of the normal to the plane and a vector in the direction of the line is equal to zero.

3. Originally Posted by mr fantastic
Two planes are perpendicular if the scalar product of their normals is equal to zero.

A line and a plane are perpendicular if the scalar product of the normal to the plane and a vector in the direction of the line is equal to zero.
When you say "scalar product" is that the same thing as "dot product"?

4. Originally Posted by DarK
When you say "scalar product" is that the same thing as "dot product"?
Yes.