Calculus and Vectors
posted by Johnny .
THE VECTORS a  5b AND ab ARE PERPENDICULAR. IF a AND b ARE UNIT VECTORS, THEN DETERMINE a dot b

(a5b).(ab) = 0 >
a^2 + 5 b^2  6 a.b = 0
a^2 = b^2 = 1 (as a and b are unit vectors), therefore:
a.b = 1