Question

Find the coordinates of the point (x,y,z) on the planez=4x+3y+1 which is closest to the origin.

Answer 1

Given plane Π : f(x,y,z) = 4x+3y-z = -1
Need to find point P on Π  that is closest to the origin O=(0,0,0).

Solution:
First step: check if O is on the plane Π : f(0,0,0)=0 ≠ -1 => O is not on Π
Next:
We know that the required point must lie on the normal vector <4,3,-1> passing through the origin, i.e. 
P=(0,0,0)+k<4,3,-1> = (4k,3k,-k)
For P to lie on plane &Pi; , it must satisfy
4(4k)+3(3k)-(-k)=-1
Solving for k
k=-1/26
=>
Point P is (4k,3k,-k) = (-4/26, -3/26, 1/26) = (-2/13, -3/26, 1/26)
because P is on the normal vector originating from the origin, and it satisfies the equation of plane &Pi;
Answer: P(-2/13, -3/26, 1/26) is the point on &Pi; closest to the origin.