At what point on the paraboloid y=x^{2}+z^{2} is the tangent plane parallel

hrostentsp6

hrostentsp6

Answered question

2021-12-06

At what point on the paraboloid
y=x2+z2
is the tangent plane parallel to the plane
x+2y+3z=1?

Answer & Explanation

Robert Harris

Robert Harris

Beginner2021-12-07Added 23 answers

We have y=x2+z2 
which is parallel to plane x+2y+3z=1 
Let F(x,y,z)=x2y+z2 
The direction vector of F, or the normal vector, is the gradient.
gradient of F=<fx,fy,fz> 
=<2x, -1,2z> 
Since F is parallel to the plane, their direction vectors are multiples of each other. c is a constant. 
<2x,-1,2z>=<1,2,3>c 
-1=2c 
c=12 
2x=c 
x=122=14 
2z=3c 
2z=3(12)=32 
z=34 
To find y, plug x and z into the original equation.
y=x2+z2=(14)2+(34)2=58 
Answer: (14,58,34) 

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