I've encountered this question but I do not know how to solve it? Help anyone? I need some clues. Find a plane through the points P1 (1,2,3) and P2(3,2,1) and perpendicular to the plane 4x - y + 2z = 7 Another question, When given point A (1,2,3) and B (3,2,1) , I'm asked to find the line equation. So If I got the direction of the line using B - A, I get the direction as (2,0,-2) I should write the line equation as (1, 2, 3) + t (2, 0, -2). My question is, instead, can I write the equation as (3, 2, 1) + t (2, 0, -2) although (3, 2, 1) is the endpoint of the line?