$$\lim _{x \rightarrow \frac{\pi}{2}}\left(\tan ^{2} x\left(\left(2 \sin ^{2} x+3 \sin x+4\right)^{\frac{1}{2}}-\left(\sin ^{2} x+6 \sin x+2\right)^{\frac{1}{2}}\right)\right)$$ बराबर है-