# Convert space curve to cartesian

1. Feb 14, 2004

### yanyin

if R = sinti+sqrt(2)costj+sintk, 0<=t<=Pi/2
please eliminate t to determine the cartesian equation of R(t). Put limits on the variables and verbally describe the curve

2. Feb 15, 2004

### himanshu121

x= sint, y=sqrt(2)cost, z=sint

u can clearly see that
x2 + y2 +z2=2{sin2t +cos2t}

=2

x2 + y2 +z2=2

3. Feb 15, 2004

### matt grime

And eqaully clearly, surely you can see there is more to it than that? You've just replaced a locally 1-d structure (a curve) with a locally 2-d structure, a sphere.

yes, the x, y, and z coordinates necessarily satisfy that, but that isn't sufficient. You need to intersect with the plane x=z (or similar) at the very least.

generally the equation is $$x=z=(1-y^2)^{1/2}/\sqrt 2$$

4. Feb 15, 2004

### yanyin

Thanks matt grime, i've checked yours is correct.
but can you show me how the above equation is reached.

5. Feb 15, 2004

### HallsofIvy

If matt grime will forgive me for sticking in my oar:

x= sint, y=sqrt(2)cost, z=sint so obviously x= z.

x2= sin2t= (1-cos2t). But
y2= 2 cos2t so cos2t= y2/2. That is x2= 1- y2/2 and