Question

Question part points submissions used find a ·
b. |a| = 40, |b| = 90, the angle between a and b is 3π/4.

Answer 1

Consider, pls, the suggested option:
1. formula is: a*b=|a||b|cos(ab);
2. a*b=40*60*cos135°=2400/√2  (≈1697,0563).