Assume that $v, w \in R$ and $∥v∥ = 2$, $∥w∥ = 3$ and $v \cdot w = -1$
Let $a = 3v−w$ and $b = v+w$. Determine $a \cdot b$
How should one approach this? I could find the vectors $v$ and $w$ if i knew the angle between them since i have their magnitudes and dot product right? The dot product is -1, isn't the angle 180 degrees then?