$14$ For steady$-$state balanced conditions the total $3-$phase power and reactive power may be expressed as

$P_e=3V_s{I}_{s}cos[{}_{ev}(0)-{}_{ei}(0)]$

$Q_e=3V_s{I}_{s}sin[{}_{ev}(0)-{}_{ei}(0)]$

Show that the following expressions are equal to those given above:

$P_e=\frac{3}{2}(V_{qs}{I}_{qs}+V_{ds}{I}_{ds})$

$Q_e=\frac{3}{2}(V_{qs}{I}_{ds}-V_{ds}{I}_{qs})$