Find the distance from the point to the plane.
point (0, 2, -1) plane 2x_1 - x_3 = 5

Solution:

Find ||proj_n AB|| where
||proj_n AB|| = ||(AB dot n_hat) n_hat||
n_hat = (1/sqrt(5), 0, 2/sqrt(5))
A = (0, 2, -1)
B = (3, 0, 1)
AB = (3, -2, 2)
||proj_n AB|| = ||[(3, -2, 2) dot (1/sqrt(5), 0, 2/sqrt(5)] n_hat||
              = ||7/sqrt(5) n_hat||
              = ||(7/5, 0, 14/5)||
              = 2sqrt(67)/5

Textbook answer: 4/sqrt(5)