b
\(\begin{array}{l}
\vec u = \hat i + 2\hat j = {u_x}\hat i + {u_y}\hat j \Rightarrow u\cos \theta  = 1,\\
u\sin \theta  = 2\\
y = x\tan \theta  - \frac{1}{2}\frac{{g{x^2}}}{{u_x^2}}\\
\therefore \,y = 2x - \frac{1}{2}g{x^2} = 2x - 5{x^2}
\end{array}\)