Question 205335:  Hi all, I asked this question recently, but did not get a response. Hopefully someone can help me this time. I need to Determine whether the the two planes; 4x+y-z = 3 and 2x - 5y + 3z =2 are parallel, orthogonal, conincident or none of these. 
Steps and notes on how to solve would be very helpful. 
Thanks, -nick 
 Answer by Alan3354(69443)      (Show Source): 
You can  put this solution on YOUR website! Determine whether the the two planes; 4x+y-z = 3 and 2x - 5y + 3z =2 are parallel, orthogonal, conincident or none of these. 
------- 
4x + y - z = 3 
Its normal vector, A, is 4i + j - k 
r = sqrt(16+1+1) = 3sqrt(2) 
-------- 
2x - 5y + 3z =2 
Its normal vector, B, is 2i - 5j + 3k 
r = sqrt(4+25+9) = sqrt(38) 
------------------- 
Finding the angle between them will clarify it. 
A dot B = |A||B|cos 
A dot B = 8-5-3 = 0 
Since the magnitudes of both A and B are non-zero, the cos = 0. 
--> 90º orthogonal 
 
  | 
 
  
 
 |   
 
 |