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Câu hỏi: Cho hai dao động điều hòa cùng phương có phương trình lần lượt là ${{x}_{1}}={{A}_{1}}\cos \left( \omega t+{{\varphi }_{1}} \right)$ và ${{x}_{2}}={{A}_{2}}\cos \left( \omega t+{{\varphi }_{2}} \right)$. Biết rằng $x={{x}_{1}}+{{x}_{2}}=A\cos \left( \omega t+\varphi \right)$. Giá trị $\varphi $ được tính theo công thức
A. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{2}}\sin {{\varphi }_{2}}}{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}$.
B. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{1}}\sin {{\varphi }_{2}}}{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}$.
C. $\tan \varphi =\dfrac{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{2}}\sin {{\varphi }_{2}}}$.
D. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}}{{{A}_{1}}\cos {{\varphi }_{1}}}+\dfrac{{{A}_{2}}\sin {{\varphi }_{2}}}{{{A}_{2}}\cos {{\varphi }_{2}}}$.
A. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{2}}\sin {{\varphi }_{2}}}{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}$.
B. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{1}}\sin {{\varphi }_{2}}}{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}$.
C. $\tan \varphi =\dfrac{{{A}_{1}}\cos {{\varphi }_{1}}+{{A}_{2}}\cos {{\varphi }_{2}}}{{{A}_{1}}\sin {{\varphi }_{1}}+{{A}_{2}}\sin {{\varphi }_{2}}}$.
D. $\tan \varphi =\dfrac{{{A}_{1}}\sin {{\varphi }_{1}}}{{{A}_{1}}\cos {{\varphi }_{1}}}+\dfrac{{{A}_{2}}\sin {{\varphi }_{2}}}{{{A}_{2}}\cos {{\varphi }_{2}}}$.
Đáp án A.