Question $1$: $(10$ Marks$)$

Consider the small disturbance steady potential flow equation,

$(1-M_{}^2){}_{}+{}_{yy}=0$

Classify the above PDE

Sketch the characteristic curves at any point $(x,y)$ if $M_{}=1\mathrm{.}1$

Where, $$ and $M_{}$ are the velocity potential and free stream Mach number, respectively.