FYI, this is all that has been proven in the chapter on the Dual Space:
$1.$ For each base there is a unique dual base.
$2.$ If $B=\{v_1,\ldots,v_n\}$ is a base and $B^*=\{\varphi_1,\ldots,\varphi_n\}$ then $(v)_B=(\varphi_1(v),\ldots,\varphi_n(v))$ and $(\varphi)_{B^*}=(\varphi(v_1),\ldots,\varphi(v_n))$.
$3.$ To each base $B_1$ in the dual there is a base $B$ with $B^*=B$.
$4.$ $\dim S^\circ+\dim S=\dim V$
$5.$ $(S+T)^\circ =S^\circ \cap T^\circ$ and $(S\cap T)^\circ=S^\circ+T^\circ$