Chọn đẳng thức sai trong các đẳng thức sau:

\[{\rm{sin}}\left( {{\rm{a + b}}} \right){\rm{ = sin}}\left( {\rm{a}} \right){\rm{cos}}\left( {\rm{b}} \right){\rm{ + cos}}\left( {\rm{a}} \right){\rm{sin}}\left( {\rm{b}} \right)\]

\[{\rm{sin}}\left( {{\rm{a + b}}} \right){\rm{ = sin}}\left( {\rm{a}} \right){\rm{cos}}\left( {\rm{a}} \right){\rm{ + cos}}\left( {\rm{b}} \right){\rm{sin}}\left( {\rm{b}} \right)\]

\[{\rm{sin}}\left( {{\rm{a}} - {\rm{b}}} \right){\rm{ = sin}}\left( {\rm{a}} \right){\rm{cos}}\left( {\rm{a}} \right) - {\rm{cos}}\left( {\rm{b}} \right){\rm{sin}}\left( {\rm{b}} \right)\]

\[{\rm{sin}}\left( {{\rm{a}} - {\rm{b}}} \right){\rm{ = sin}}\left( {\rm{b}} \right){\rm{cos}}\left( {\rm{a}} \right) - {\rm{cos}}\left( {\rm{a}} \right){\rm{sin}}\left( {\rm{b}} \right)\]