## Precalculus (6th Edition) Blitzer

a. $5i+23j$ b. $-12$
a. Given $\vec v=2i+7j$ and $\vec w=i-2j$, we have $3\vec v-\vec w=3(2i+7j)-(i-2j)=5i+23j$ b. We have $\vec v\cdot \vec w=(2i+7j)\cdot(i-2j)=(2)(1)+(7)(-2)=-12$