Question

if 2x x 2x= 4x square then why not cos thita x cos thita = cos square thita square

Answer 1

2x * 2x = 4x
Means
2*x*2*x
= 2*2*x*x
=4*x*x

But
Cos(theta)*cos(theta) is not same as
Cos * theta * Cos * theta

Thats why
Cos(theta) * Cos(theta) = Cos^2(theta)