4.下列各式从左边到右边的变形,属于因式分解的是( )
| A. | (x+y)2=x2+2xy+y2 | B. | 2x2-8=2(x+2)(x-2) | ||
| C. | 2x2-2x+1=2x(x-1)+1 | D. | (x+1)(x-1)=x2-1 |
3.式子(2x+y)(-2x+y)的运算结果是( )
| A. | 2x2-y2 | B. | y2-4x2 | C. | 4x2-y2 | D. | y2-2x2 |
2.下列式子中,正确的是( )
| A. | x3•x5=x15 | B. | (-x3)2=x9 | C. | (3x2y)2=3x4y | D. | (-2x2y)2=4x4y2 |
1.下列四张扑克牌中,属于中心对称的图形是( )

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| A. | 红桃7 | B. | 方块4 | C. | 梅花6 | D. | 黑桃5 |