1.

If sin x + sin y = a and cos x + cos y = b, then \({\tan ^2}\left( {\frac{{{\rm{x}} + {\rm{y}}}}{2}} \right) + {\tan ^2}\left( {\frac{{{\rm{x}} - {\rm{y}}}}{2}} \right)\) is equal to

A. \(\frac{{{{\rm{a}}^4} + {{\rm{b}}^4} + 4{{\rm{b}}^2}}}{{{{\rm{a}}^2}{{\rm{b}}^2} + {{\rm{b}}^4}}}\)
B. \(\frac{{{{\rm{a}}^4} - {{\rm{b}}^4} + 4{{\rm{b}}^2}}}{{{{\rm{a}}^2}{{\rm{b}}^2} + {{\rm{b}}^4}}}\)
C. \(\frac{{{{\rm{a}}^4} - {{\rm{b}}^4} + 4{{\rm{a}}^2}}}{{{{\rm{a}}^2}{{\rm{b}}^2} + {{\rm{a}}^4}}}\)
D. None of the above
Answer» C. \(\frac{{{{\rm{a}}^4} - {{\rm{b}}^4} + 4{{\rm{a}}^2}}}{{{{\rm{a}}^2}{{\rm{b}}^2} + {{\rm{a}}^4}}}\)


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