1. The problem statement, all variables and given/known data Find the angle between the plane 3x+5y+7z = 1 and the plane z = 0. 2. Relevant equations a.b=|a||b|cosθ 3. The attempt at a solution Hi, I know that I need to have both these planes in the form (x,y,z) and then find the dot product to find the angle between them. The problem I am having is with putting them in that form, at first I assumed plane 1 would just be (3,5,7) and plane 2 would be (0,0,1), but I have also read that to find the angle between to planes I need the normal vector to each plane, and this has confused me. Using these vectors I came up with the answer 30.8°, but I don't know if what I did was right! Any help would be appreciated!