cross product question?

Question

I'm trying to find the equation of a plane containing the point (1,2,1) and perpendicular to the planes ( x + y = 2) and (2x + y - z = 1)

I think the answer should be -(x-1) + (y - 2) - (z+) = 0 but the answer in the book reverses the signs so that
(x - 1) - (y-2) - (z+1) = 0

I have no idea why?
thanks

Answer 1

It doesn't matter. X your equation by -1 then the result is the same. It is because it describe the same plane.