If 2 2 22 22 2 2 ua b a b = q+ q+ q+ q cos sin sin cos then the difference between the maximum and minimum values of u 2 is given by

If $u=\sqrt{a^{2} \cos ^{2} \theta+b^{2} \sin ^{2} \theta}+\sqrt{a^{2} \sin ^{2} \theta+b^{2} \cos ^{2} \theta}$ then the difference between the maximum and minimum values of $u^{2}$ is given by