The "distributive law", in any algebraic system in which we have definitions of "addition" and "multiplication", says that a(b+ c)= ab+ ac. That's probably shown on page 676. And I would suggest that what they "asking you to do" is exactly what they said:
Let \(\displaystyle \vec{u}= <a_1, b_1, c_1>\), [itex]\vec{v}= <a_2, b_2, c_2>[/tex], and \(\displaystyle \vec{w}= <a_3, b_3, c_3>\).
Now, in terms of those, what is \(\displaystyle \vec{v}+ \vec{w}\)? What is \(\displaystyle \vec{u}\cdot)(\vec{v}+ \vec{w})\)?
What is \(\displaystyle \vec{u}\cdot\vec{v}\)? What is \(\displaystyle \vec{u}\cdot\vec{w}\)?
What is \(\displaystyle \vec{u}\cdot\vec{v}+ \vec{u}\cdot\vec{w}\)?