posted by Alice .
Which 3 x 3 matrix represents a reflection in the yz plane followed by inversion through the origin?
That would be the product of the matrices of the two operations, done in that order. The first matrix changes x tp -x, and leaves y and z the same. The second matrix changes x to -x, y to -y and z to -z.
The product matrix leaves x unchanged and changes y to -y and z to -z.
The resulting matrix would seem to be