Chapter 9.2, Problem 4P

Problems

For Problems 1-5, show that the given vector functions are linearly independent on 
 $\left(-\infty ,\infty \right)$.

 $x_1\left(t\right)=\left[\begin{array}{c}t\\ t\end{array}\right]$, 
 $x_2\left(t\right)=\left[\begin{array}{c}\left|t\right|\\ t\end{array}\right]$.

Is there an interval on which 
 $x_1\left(t\right)$ and 
 $x_2\left(t\right)$ in this exercise are not linearly independent?