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Câu hỏi: Với mọi số thực $a\ne 0$, ${{\log }_{2}}\left( 4{{a}^{2}} \right)$ bằng
A. $2\left( 1+{{\log }_{2}}\left| a \right| \right)$.
B. $2-{{\log }_{2}}a$.
C. $2+{{\log }_{2}}\left| a \right|$.
D. $2+{{\log }_{2}}a$.
A. $2\left( 1+{{\log }_{2}}\left| a \right| \right)$.
B. $2-{{\log }_{2}}a$.
C. $2+{{\log }_{2}}\left| a \right|$.
D. $2+{{\log }_{2}}a$.
Ta có ${{\log }_{2}}\left( 4{{a}^{2}} \right)={{\log }_{2}}{{\left( 2a \right)}^{2}}=2{{\log }_{2}}\left| 2a \right|=2.\left( {{\log }_{2}}2+{{\log }_{2}}\left| a \right| \right)=2.\left( 1+{{\log }_{2}}\left| a \right| \right)$.
Đáp án A.