Solution (source code)

= Solution

For the <B2 root system> with $\alpha_1$ short, the positive roots are
$$
\alpha_1,\quad\alpha_2,\quad\alpha_1+\alpha_2,\quad2\alpha_1+\alpha_2.
$$
Substituting $\lambda=a\omega_1+b\omega_2$ into the <Weyl dimension formula for B2> gives
$$
\boxed{\dim V(a\omega_1+b\omega_2)
=\frac{(a+1)(b+1)(a+b+2)(a+2b+3)}6.}
$$