9.下列计算正确的是( )
| A. | (x+y)(y-x)=x2-y2 | B. | (x-2y)(x+2y)=x2-2y2 | ||
| C. | (2x-$\frac{1}{2}$y)2=4x2-2xy+$\frac{1}{4}$y2 | D. | (-3x-2y)2=9x2-12xy+4y2 |
7.某数的平方根为2a+3与a-15,这个数是( )
| A. | 121 | B. | 11 | C. | ±11 | D. | 4 |
4.化简5a•(2a2-ab),结果正确的是( )
| A. | -10a3-5ab | B. | 10a3-5a2b | C. | -10a2+5a2b | D. | -10a3+5a2b |
2.在△ABC中,AB=BC=AC=6,则△ABC的面积为( )
0 282056 282064 282070 282074 282080 282082 282086 282092 282094 282100 282106 282110 282112 282116 282122 282124 282130 282134 282136 282140 282142 282146 282148 282150 282151 282152 282154 282155 282156 282158 282160 282164 282166 282170 282172 282176 282182 282184 282190 282194 282196 282200 282206 282212 282214 282220 282224 282226 282232 282236 282242 282250 366461
| A. | 9 | B. | 18 | C. | 9$\sqrt{3}$ | D. | 18$\sqrt{3}$ |