# Vector function of two arguments

• Oct 13th 2008, 09:55 AM
ScullyX51
Vector function of two arguments
⃗r : U → R3 ,U ⊂ R 2
We are given:
⃗r (u,v)= (√v/2 cosh u, √v2sinhu,v)
or the same as:
x= √v/2 cosh u
y- √vsinh u
z=u

The question is verify that the points r(u,v) satisfy the equation z= 4x^2-y^2. And identify what kind of surface z=4x^2-y^2 is.

This is what I did:
I identified the surface given by the equation z=4x^2-y^2 as a hyperbolic parabloid.

The part I am confused about is showing that it satisfies the equation. what I did is substituted the given values of x,y,and z into this formula, and I got:
v= vcsosh^2u-sin^2u
I don't know where to go from here, would appreciate any suggestions.
• Oct 13th 2008, 03:51 PM
WantMath
Hi,

the way you worte it looks a little confusing.

so as far as I understind is:

x=SQRT(v/2)*cosh(u)
y=SQRT(2v)*sinh(u)

then
4*x^2=4*v/2*(cosh(u))^2
y^2=2v*(sinh(u))^2

and 4*x^2-y^2=2v*(cosh(u))^2-2v*(sinh(u))^2=2v*((cosh(u))^2-(sinh(u))^2)=2v
• Oct 13th 2008, 04:54 PM
ScullyX51
Thank you so much!