Linear transformation: reflection of R³ in the (x,z)-plane

[mathmathmad]

Homework Statement

find the matrices representing linear map T:R3 -> R3 with respect to the standard basis

Homework Equations

T reflects each point in the (x,z)-plane

The Attempt at a Solution

I can't figure out how does x,z plane looks like...

 

[Dick]

The xz plane is the plane y=0.