15.下列函数求导运算正确的是( )
①(3x)′=3xlog3e;②(log2x)′=$\frac{1}{x•ln2}$;③(x•ex)′=ex+1;④($\frac{1}{lnx}$)′=x.
①(3x)′=3xlog3e;②(log2x)′=$\frac{1}{x•ln2}$;③(x•ex)′=ex+1;④($\frac{1}{lnx}$)′=x.
A. | ① | B. | ② | C. | ③ | D. | ④ |
14.设某批产品合格率为$\frac{3}{4}$,不合格率为$\frac{1}{4}$,现对该产品进行测试,设第ξ次首次测到正品,则P(ξ=3)=( )
A. | ${(\frac{1}{4})^2}×(\frac{3}{4})$ | B. | ${(\frac{3}{4})^2}×(\frac{1}{4})$ | C. | $C_3^2{(\frac{1}{4})^2}×(\frac{3}{4})$ | D. | $C_3^2{(\frac{3}{4})^2}×(\frac{1}{4})$ |
13.已知向量$\overrightarrow{a}$和$\overrightarrow{b}$的夹角为120°,|$\overrightarrow{a}$|=1,|$\overrightarrow{b}$|=3,则|$\overrightarrow{a}$-$\overrightarrow{b}$|=( )
0 247963 247971 247977 247981 247987 247989 247993 247999 248001 248007 248013 248017 248019 248023 248029 248031 248037 248041 248043 248047 248049 248053 248055 248057 248058 248059 248061 248062 248063 248065 248067 248071 248073 248077 248079 248083 248089 248091 248097 248101 248103 248107 248113 248119 248121 248127 248131 248133 248139 248143 248149 248157 266669
A. | 2$\sqrt{3}$ | B. | $\sqrt{15}$ | C. | 4 | D. | $\sqrt{13}$ |