5.若实数a和b满足a2+4b2=1,则$\frac{2ab}{|a|+2|b|}$的最大值为( )
A. | $\frac{2\sqrt{5}}{15}$ | B. | $\frac{\sqrt{2}}{4}$ | C. | $\frac{\sqrt{5}}{5}$ | D. | $\frac{\sqrt{2}}{2}$ |
4.复数$\frac{5}{2-i}$的共轭复数是( )
A. | 2+i | B. | 2-i | C. | $\frac{10}{3}$+$\frac{5}{3}$ | D. | $\frac{10}{3}$$-\frac{5}{3}$ |
1.已知log11[log3(log2x)]=0,则x${\;}^{-\frac{1}{2}}$=( )
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A. | $\frac{1}{3}$ | B. | $\frac{1}{2\sqrt{3}}$ | C. | $\frac{1}{2\sqrt{2}}$ | D. | $\frac{1}{3\sqrt{3}}$ |