If vec(a)andvec(b) are two unit vectors such that vec(a) + 2vec(b) and 5vec(a) - 4vec(b) are perpendicupar to each other, then the angle between vec(a) and vec(b) is

If vec(a)andvec(b) are two unit vectors such that vec(a) + 2vec(b) and

1.	If vec(a)andvec(b) are two unit vectors such that vec(a) + 2vec(b) and 5vec(a) - 4vec(b) are perpendicupar to each other, then the angle between vec(a) and vec(b) is
Answer» SOLUTION :`(vec(a)+2vec(b)).(5vec(a)-4vec(b))=0` `5a^(2)4abcostheta+10abcostheta-8b^(2)=0` `=5-4 cos THETA+10costheta-8=0[a=b=1]` `= - 3 + 6 cos theta = 0` `cos theta = 1//2, theta = 60^(@)`