What is the angle between the straight lines (m2 - mn)y = (mn + n2)x + n3 and (mn + m2) y = (mn - n2)x + m3, where m > n?

\({\tan ^{ - 1}}\left( {\frac{{4{{\rm{m}}^2}{{\rm{n}}^2}}}{{{{\rm{m}}^4} + {{\rm{n}}^4}}}} \right)\)

\({\tan ^{ - 1}}\left( {\frac{{2{\rm{mn}}}}{{{{\rm{m}}^2} + {{\rm{n}}^2}}}} \right)\)

\({\tan ^{ - 1}}\left( {\frac{{4{{\rm{m}}^2}{{\rm{n}}^2}}}{{{{\rm{m}}^4} - {{\rm{n}}^4}}}} \right)\)

What is the angle between the straight lines (m2 - mn)y = (mn + n2)x +

1.	What is the angle between the straight lines (m2 - mn)y = (mn + n2)x + n3 and (mn + m2) y = (mn - n2)x + m3, where m > n?
A.	\({\tan ^{ - 1}}\left( {\frac{{2{\rm{mn}}}}{{{{\rm{m}}^2} + {{\rm{n}}^2}}}} \right)\)
B.	\({\tan ^{ - 1}}\left( {\frac{{4{{\rm{m}}^2}{{\rm{n}}^2}}}{{{{\rm{m}}^4} - {{\rm{n}}^4}}}} \right)\)
C.	\({\tan ^{ - 1}}\left( {\frac{{4{{\rm{m}}^2}{{\rm{n}}^2}}}{{{{\rm{m}}^4} + {{\rm{n}}^4}}}} \right)\)
D.	45°
Answer» C. \({\tan ^{ - 1}}\left( {\frac{{4{{\rm{m}}^2}{{\rm{n}}^2}}}{{{{\rm{m}}^4} + {{\rm{n}}^4}}}} \right)\)