Cho \[{\rm{sin}}\left( {\rm{\alpha }} \right){\rm{ + cos}}\left( {\rm{\beta }} \right){\rm{ = }}\frac{{\rm{5}}}{{\rm{4}}}\], khi đó \(\sin \left( {2\alpha } \right)\)có giá trị bằng:

A. 30⁰

B. 90⁰

C. 60⁰

D. 40⁰

A. \[\frac{{\sqrt 3 }}{6} - \frac{{\sqrt 2 }}{2}\]

B. \[\frac{{\sqrt 3 }}{3} + \frac{1}{2}\]

C. \[\frac{{\sqrt 3 }}{3} - \frac{1}{2}\]

D. \[\frac{{\sqrt 3 }}{6} + \frac{{\sqrt 2 }}{2}\]

A. \[{\rm{cos}}\left( {{\rm{a + }}\frac{{\rm{\pi }}}{{\rm{3}}}} \right){\rm{ = cos}}\left( {\rm{a}} \right){\rm{ + }}\frac{{\rm{1}}}{{\rm{2}}}\]

B. \[{\rm{cos}}\left( {{\rm{a + }}\frac{{\rm{\pi }}}{{\rm{3}}}} \right){\rm{ = }}\frac{{\rm{1}}}{{\rm{2}}}{\rm{sin}}\left( {\rm{a}} \right) - \frac{{\sqrt {\rm{3}} }}{{\rm{2}}}{\rm{cos}}\left( {\rm{a}} \right)\]

C. \[{\rm{cos}}\left( {{\rm{a + }}\frac{{\rm{\pi }}}{{\rm{3}}}} \right){\rm{ = }}\frac{{\sqrt {\rm{3}} }}{{\rm{2}}}{\rm{sin}}\left( {\rm{a}} \right) - \frac{{\rm{1}}}{{\rm{2}}}{\rm{cos}}\left( {\rm{a}} \right)\]

D. \[{\rm{cos}}\left( {{\rm{a + }}\frac{{\rm{\pi }}}{{\rm{3}}}} \right){\rm{ = }}\frac{{\rm{1}}}{{\rm{2}}}{\rm{cos}}\left( {\rm{a}} \right) - \frac{{\sqrt {\rm{3}} }}{{\rm{2}}}{\rm{sin}}\left( {\rm{a}} \right)\]

A. S = 17

B. \[{\rm{S = }}\frac{{{\rm{17}}}}{{\rm{2}}}\]

C. S = 1

D. S = 0

A. \[\widehat A{\rm{ = }}\widehat B{\rm{ = }}\widehat C{\rm{ = 6}}{{\rm{0}}^{\rm{0}}}\]

B. \[\widehat A{\rm{ = 9}}{{\rm{0}}^0}{\rm{; }}\widehat B{\rm{ = 6}}{{\rm{0}}^{\rm{0}}};\,\,\widehat C{\rm{ = 3}}{{\rm{0}}^{\rm{0}}}\]

C. \[\widehat A{\rm{ = 9}}{{\rm{0}}^0}{\rm{; }}\widehat B{\rm{ = 3}}{{\rm{0}}^{\rm{0}}};\,\,\widehat C{\rm{ = 6}}{{\rm{0}}^{\rm{0}}}\]

D. \[\widehat A{\rm{ = 9}}{{\rm{0}}^0}{\rm{; }}\widehat B{\rm{ = 4}}{{\rm{5}}^{\rm{0}}};\,\,\widehat C{\rm{ = 45}}{{\rm{0}}^{\rm{0}}}\]

A. \[{\rm{sin}}\left( {{\rm{2a}}} \right){\rm{ = 2sin}}\left( {\rm{a}} \right){\rm{cos}}\left( {\rm{a}} \right)\]

B. \[{\rm{sin}}\left( {{\rm{2a}}} \right){\rm{ = sin}}\left( {\rm{a}} \right){\rm{cos}}\left( {\rm{a}} \right)\]

C. \[{\rm{cos}}\left( {{\rm{2a}}} \right){\rm{ = co}}{{\rm{s}}^{\rm{2}}}\left( {\rm{a}} \right) - {\rm{si}}{{\rm{n}}^{\rm{2}}}\left( {\rm{a}} \right)\]

D. \[{\rm{cos}}\left( {{\rm{2a}}} \right){\rm{ = 1}} - {\rm{2si}}{{\rm{n}}^{\rm{2}}}\left( {\rm{a}} \right)\]

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

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

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

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