Normalize the vectors (create unit vectors in the same directions).
The diagram shows each vector after it has been normalized. (Remember, this means creating a unit vector in the same direction as the original vector).
Recall that a subscript u indicates a unit vector: bu.
Now which dot product is larger? au · bu , or au · cu ?
Hint: remember that u · v = |u||v| cos θ. But now both vectors have length 1.0.