7.在△ABC中,∠A=90°,AB=3,BC=5,则sinB的值是( )
| A. | $\frac{4}{3}$ | B. | $\frac{3}{4}$ | C. | $\frac{4}{5}$ | D. | $\frac{3}{5}$ |
5.下列运算正确的是( )
| A. | a3•a2=a6 | B. | $\sqrt{9}$=3 | C. | (a2)3=a5 | D. | 4a-2a=2 |
4.下列运算中,不正确的是( )
| A. | a8•a2=a10 | B. | a6÷a2=a4 | C. | (a2)3=a6 | D. | (-3a2b4)3=-27a6b7 |
2.下列运算中,结果等于a5的是( )
| A. | a2+a3 | B. | a10÷a2 | C. | a3•a2 | D. | (a2)3 |
20.下列运算正确的是( )
| A. | 3a2-a2=2 | B. | a2•a3=a6 | C. | (-a2)2=a4 | D. | (a+1)2=a2+1 |
19.下列运算错误的是( )
0 282933 282941 282947 282951 282957 282959 282963 282969 282971 282977 282983 282987 282989 282993 282999 283001 283007 283011 283013 283017 283019 283023 283025 283027 283028 283029 283031 283032 283033 283035 283037 283041 283043 283047 283049 283053 283059 283061 283067 283071 283073 283077 283083 283089 283091 283097 283101 283103 283109 283113 283119 283127 366461
| A. | a4•a3=a7 | B. | a4-a3=a | C. | (a4)3=a12 | D. | (ab)3=a3b3 |