Find the angle between the planes :

x – y + z = 5 and x + 2y + z = 9

Given planes are x – y + z = 5 and x + 2y + z = 9


We know that angle between two planes,


a1x + b1y + c1z + d1 = 0


a2x + b2y + c2z + d2 = 0 is given as



Here we have,


a1 = 1, b1 = – 1, c1 = 1


a2 = 1, b2 = 2, c2 = 1







Hence, the angle between planes x – y + z = 5 and x + 2y + z = 9 is


2