A linear system may have a unique solution, no solution, or infinitely many solutions. Indicate the type of the system for the following examples by U , N , or I , respectively.
1. $\begin{array}{rrcl}2x-3y&=&5\\ 4x-6y &=& 10\\ \end{array}$
2. $\begin{array}{rrcl}2x+3y&=&1\\ 4x+6y &=& 1\\ \end{array}$
3. $\begin{array}{rrcl}2x+3y&=&0\\ 2x+4y &=& 0\\ \end{array}$
4. $\begin{array}{rrcl}x+y&=&5\\ x+2y &=& 10\\ \end{array}$
5. $\begin{array}{rrcl}7x+3y&=&\pi\\ 4x-6y &=& \pi^2\\ \end{array}$