May 19th, 2017, 01:30 AM  #1 
Senior Member Joined: Nov 2015 From: hyderabad Posts: 167 Thanks: 2  Planes
The locus of a point $P$ which is at the same distance from two planes $x+y+z=1$ , $z=0$ is a) an unbounded set. b) a sphere. c) a pair of parallel planes. d) a pair of intersecting planes. Im guessing this could be intersecting of planes! Someone correct me If I'm wrong 
May 20th, 2017, 02:18 AM  #2 
Math Team Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,347 Thanks: 224 
I think you are correct 
May 20th, 2017, 04:05 AM  #3 
Math Team Joined: Jan 2015 From: Alabama Posts: 2,576 Thanks: 668 
The two given planes intersect along a straight line. Take any point along that straight line and construct the plane containing that point perpendicular to the two given planes. The two given planes intersect in this third plane in two straight lines intersecting at that point. That makes four angles, two pair of "vertical angles". Bisecting each pair gives the two planes that are "at the same distance from the two planes".

May 20th, 2017, 05:27 AM  #4 
Member Joined: Jan 2016 From: Athens, OH Posts: 45 Thanks: 26 
Analytically, this is easy. Let P=(x,y,z) be equidistant from the 2 planes. Then $${x+y+z1\over \sqrt3}=z$$ So $$(x+y+z1)^2=3z^2$$ Thus $$(x+y+z1\sqrt3z)(x+y+z1+\sqrt3z)=0$$ Hence $$P\text{ is on } x+y+(1\sqrt3)z1=0\text{ or P is on } x+y+(1+\sqrt3)z1=0$$ These two planes are not parallel since they have nonparallel normals; so they intersect. Conversely, if P is on either plane, the above steps are reversible and so P is equidistant from the original two planes. 

Tags 
planes 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Planes  Swami Mathsananda  Math  1  September 16th, 2015 12:53 PM 
Planes and Spheres  lilstef  Geometry  10  June 23rd, 2014 10:00 AM 
Planes and lines in 3D  Cyberdollar  Geometry  6  June 13th, 2014 11:04 AM 
Planes  gaussrelatz  Algebra  3  October 7th, 2013 09:26 AM 
Intersection of two planes in R3  majami  Linear Algebra  1  October 2nd, 2010 10:18 AM 