Question

Find the angle between the vectors a and b such that 2a + b = i + j and a + 2b = i – j.

Answer 1

Given 2a + b = i + j and a + 2b = i – j 

Solving, we get

a = (1/3)(i + 3j) and b = (1/3)(i – 3j) 

Since, 

a.b = ab cos(θ)