18.观察下列前三个式子:$\sqrt{{3}^{2}-1}$=$\sqrt{2}$×$\sqrt{4}$,$\sqrt{{4}^{2}-1}$=$\sqrt{3}$×$\sqrt{5}$,$\sqrt{{5}^{2}-1}$=$\sqrt{4}$×$\sqrt{6}$,…,按照这样的规律第10个式子的结果是( )
| A. | $\sqrt{9}$×$\sqrt{11}$ | B. | $\sqrt{10}$×$\sqrt{12}$ | C. | $\sqrt{11}$×$\sqrt{13}$ | D. | $\sqrt{12}$×$\sqrt{14}$ |
17.下列二次根式中属于最简二次根式的是( )
| A. | $\sqrt{18}$ | B. | $\sqrt{{a}^{2}b}$ | C. | $\sqrt{{x}^{2}+1}$ | D. | $\sqrt{\frac{x+1}{5}}$ |
16.下列各式计算正确的是( )
0 308947 308955 308961 308965 308971 308973 308977 308983 308985 308991 308997 309001 309003 309007 309013 309015 309021 309025 309027 309031 309033 309037 309039 309041 309042 309043 309045 309046 309047 309049 309051 309055 309057 309061 309063 309067 309073 309075 309081 309085 309087 309091 309097 309103 309105 309111 309115 309117 309123 309127 309133 309141 366461
| A. | $\sqrt{{2}^{2}+{3}^{2}}$=2+3 | B. | 3$\sqrt{2}$+5$\sqrt{3}$=8$\sqrt{6}$ | ||
| C. | $\sqrt{1{5}^{2}-1{2}^{2}}$=$\sqrt{15+12}$×$\sqrt{15-12}$ | D. | $\sqrt{4\frac{1}{2}}$=2$\sqrt{\frac{1}{2}}$ |