11.抛物线y=2x2-4x+5的对称轴是( )
| A. | x=2 | B. | x=-1 | C. | x=-2 | D. | x=1 |
10.在Rt△ABC中,∠C=90°,a=5,b=12,则cosA的值为( )
0 278927 278935 278941 278945 278951 278953 278957 278963 278965 278971 278977 278981 278983 278987 278993 278995 279001 279005 279007 279011 279013 279017 279019 279021 279022 279023 279025 279026 279027 279029 279031 279035 279037 279041 279043 279047 279053 279055 279061 279065 279067 279071 279077 279083 279085 279091 279095 279097 279103 279107 279113 279121 366461
| A. | $\frac{12}{13}$ | B. | $\frac{12}{17}$ | C. | $\frac{5}{13}$ | D. | $\frac{5}{17}$ |