下列运算正确的是( )．
A: x2+x2=x4
B: (a-1)2=a2-1
C: a2·a3=a5。
D: 3x+2y=5xy
A: x2+x2=x4
B: (a-1)2=a2-1
C: a2·a3=a5。
D: 3x+2y=5xy
举一反三
- 下列对二维数组的定义和初始化正确的是( )。 A: int x,a[x][x] = {1, 2, 3, 4 , 5}; B: int a[1][2] = {1, 2, 3, 4, 5}; C: int a[2][2] = { {1, 2}, {2, 3} }; D: float a[][2] = {1, 2, 3, 4, 5};
- 执行以下语句的结果：dict1={"x":1,"y":2,"z":3}dict2={"x":4,"a":5}dict1.update(dict2) A: {"x":1,"y":2,"z":3,"x":4,"a":5} B: {"x":4,"a":5,"x":1,"y":2,"z":3} C: 有重复项，结果有误！ D: {"x":4,"y":2,"z":3,"a":5}
- 执行y=[x for x in range(5) if x%2==1]后,y结果是( )。 A: [1, 3, 5] B: [0, 2, 4] C: [1, 3] D: [2, 4]
- 青书学堂: 二次型 f( x 1 , x 2 , x 3 )=2 x 1 2 +5 x 2 2 +5 x 3 2 +4 x 1 x 2 −8 x 2 x 3 ，则 f的矩阵为 。
- 分解因式()x()3()y()-()2()x()2()y()2()+()xy()3()正确的是A.()xy()(()x()+()y())()2()B.()xy()(()x()2()﹣()2()xy()+()y()2())()C.()xy()(()x()2()+2()xy()﹣()y()2())()D.()xy()(()x()﹣()y())()2