A.\(A = \sqrt {A_1^2 + A_2^2 + 2{A_1}{A_2}co{\rm{s}}\left( {{\varphi _1} - {\varphi _2}} \right)} \)
B.\(A = \sqrt {A_1^2 + A_2^2 - 2{A_1}{A_2}co{\rm{s}}\left( {{\varphi _1} - {\varphi _2}} \right)} \)
C.\(A = \sqrt {{A_1} + {A_2} + 2{{\rm{A}}_1}{A_2}co{\rm{s}}\left( {{\varphi _1} - {\varphi _2}} \right)} \)
D.\(A = \sqrt {{A_1} + {A_2} - 2{A_1}{A_2}co{\rm{s}}\left( {{\varphi _1} - {\varphi _2}} \right)} \)  

Các câu hỏi liên quan