Question 61

Q61. If cos A – sin A = m and cos A + sin A = n, show that 

           $\frac{{\mathrm{m}}^2-{\mathrm{n}}^2}{{\mathrm{m}}^2+{\mathrm{n}}^2}=-2 \sin \mathrm{A} \cos \mathrm{A} = \frac{2}{\tan \mathrm{A} +\cot \mathrm{A}}$.