اگر $\alpha +\beta ={{135}^{{}^\circ }}$ و $\tan \left( \alpha -\beta \right)=\frac{3}{4}$، مقدار کسر $\frac{{{\cos }^{2}}\alpha {{\cos }^{2}}\beta -{{\sin }^{2}}\alpha {{\sin }^{2}}\beta }{{{\sin }^{2}}\alpha {{\cos }^{2}}\beta -{{\cos }^{2}}\alpha {{\sin }^{2}}\beta }$ کدام است؟