content_image/324674.jpg content_image/324673.jpg content_image/324670.jpg content_image/324671.jpg content_image/324672.jpg content_image/324669.jpg content_image/324666.jpg content_image/324668.jpg
<img src='content_image/324674.jpg'>

Thus, we get 

<img src='content_image/324673.jpg'>

where 

<img src='content_image/324670.jpg'>

<img src='content_image/324671.jpg'>

<img src='content_image/324672.jpg'>

This follows that n$_{1}$ ( s ) //n ( s, t$_{0}$ ), L$_{1}$ ≤ s ≤ L$_{2}$ , if and only if there exits a function λ ( s ) ̸ = 0 such that 

<img src='content_image/324669.jpg'>

Secondly, since S ( T ) = ωT, ω ̸ = 0 , we obtain 

where s$_{0}$ is the starting value of the arc-length and θ = θ ( s ) . In this paper, we assume that s$_{0}$ = 0 . 

Combining (3.2), (3.3) and (3.4), we have the following theorem. 

Theorem 3 A spacelike curve r ( s ) with spacelike binormal is a line of curva- ture on the surface P ( s, t ) if and only if the followings are satisfied: 

<img src='content_image/324666.jpg'>

<img src='content_image/324668.jpg'>

