[填空题]
Five equilateral triangms89lcb8w we/,g*:la ,miip*hv b8o kles, each with side len ;xfa h0o0j8swgth 4 cm, are arranged to form a truss bridge model.This is shown in the xf;a80ow s0hj following diagram.
The vectors $ \mathbf{a}, \mathbf{b}$ and $\mathbf{c}$ are shown on the diagram.
Find $\mathbf{a} \cdot(\mathbf{a}+\mathbf{b}+2 \mathbf{c}) $.
