2.$3(\frac{1}{\cos x^{2}}+\cot x^{2})+4(\frac{\sin x}{\cos x}+\frac{\cos x}{\sin x})-1=0$$\Leftrightarrow 3(\frac{1}{\cos x^{2}}+\frac{\cos x^{2}}{\sin x^{2}})+\frac{4}{sinx.cosx}-1=0$
$\Leftrightarrow \frac{3}{\sin x^{2}\cos x^{2}}+\frac{4}{sinx.cosx}-\frac{\sin x^{2}\cos x^{2}}{\sin x^{2}\cos x^{2}}=0$
$\Leftrightarrow \frac{3+4sinxcosx-\sin x^{2}\cos x^{2}}{\sin x^{2}\cos x^{2}}=0$
$\Rightarrow 3+4\sin x\cos x-\sin x^{2}\cos x^{2}=0$
$\Leftrightarrow -(\sin x^{2}\cos x^{2}-4\sin x\cos x+4)+7=0$
$\Leftrightarrow (\sin x\cos x-2)^{2}=7$
$\Rightarrow \sin x\cos x-2=\sqrt{7} hoặc \sin x\cos x-2=-\sqrt{7}$
$\Leftrightarrow \sin x\cos x=\sqrt{7}+2 hoăc sinxcosx=-\sqrt{7}+2$
TA có: $-1\leq\sin x\leq 1$ và $-1\leq \cos x\leq 1$
$\Rightarrow -1\leq \sin x\cos x\leq 1$ nên PT này vô nghiệm