Work Step by Step
Given: $ a = (p,-p, 2p)$ and $b=(2q,q,-q)$ $ a \cdot b=p \cdot 2q+(-p) \cdot q+ 2p \cdot q$ $a \cdot b=p \cdot 2q+(-p) \cdot q+ 2p \cdot q=2pq-pq-2pq$ $=-pq$
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