\begin{equation}
 B_i(t)=\frac{1}{h^3} \left \{ \begin{array}{r1}
 
 h^3+3h^2(t-t_{i-1})+3h(t-t_{i-1})-3(t-t_{i-1}) & t\in[t_{i-2},t_{i-1})\\

h^3+3h^2(t_{i+1}-t)+3h(t_{i+1}-t)-3(t_{i+1}-t)& t\in[t_{i-2},t_{i-1})\\

{(t_{i+2}-t)}^3  & t\in[t_{i-2},t_{i-1})\\
     0 & otherwise \nonumber

\end{array} \Right
 \end{equation}