18.在下列各数中:3.1415926,$\sqrt{\frac{49}{100}}$,0.2,$\sqrt{7}$,$\frac{13}{11}$,$\root{3}{27}$,无理数的个数是( )
| A. | 1 | B. | 2 | C. | 3 | D. | 4 |
15.方程组$\left\{\begin{array}{l}{x+y=3}\\{x-y=1}\end{array}\right.$的解为( )
| A. | $\left\{\begin{array}{l}{x=3}\\{y=0}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x=3}\\{y=2}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x=-1}\\{y=-2}\end{array}\right.$ |
13.已知点P1(a-1,4)和P2(2,b)关于x轴对称,则(a+b)2015的值为( )
0 281076 281084 281090 281094 281100 281102 281106 281112 281114 281120 281126 281130 281132 281136 281142 281144 281150 281154 281156 281160 281162 281166 281168 281170 281171 281172 281174 281175 281176 281178 281180 281184 281186 281190 281192 281196 281202 281204 281210 281214 281216 281220 281226 281232 281234 281240 281244 281246 281252 281256 281262 281270 366461
| A. | 72014 | B. | 1 | C. | -1 | D. | (-3)2014 |