linear quadratic problem

例句：

1. 1.The path is linear and easy to follow.
   这条路线是直线的，很容易跟随。
2. 2.The line of the road is linear.
   路的线条是直线的。
3. 3. The linearity of the equation is important for solving problems.
   方程的线性性质对于解决问题很重要。