\frac{\partial}{\partial x}\right) u=0 \\ \bigcirc\left(\frac{\partial u}{\partial t}+c \frac{\partial u}{\partial x}\right)^{2}=0 \\ \bigcirc\left(\frac{\partial u}{\partial t}+c \frac{\partial u}{\partial x}\right)\left(\frac{\partial u}{\partial t}-c \frac{\partial u}{\partial x}\right)=0 \\ \bigcirc\left(\frac{\partial u}{\partial t}+c \frac{\partial u}{\partial x}\right)\left(\frac{\partial u}{\partial t}+c \frac{\partial u}{\partial x}\right)=0 \end{array}
Fig: 1
Fig: 2