9.半径为1的圆中有一条弦,如果它的长为$\sqrt{3}$,那么这条弦所对的圆周角为( )
| A. | 60° | B. | 120° | C. | 45° | D. | 60°或120° |
3.已知a+b=10,ab=-2,则(3a-2b)-(ab-5b)的值为( )
| A. | 28 | B. | 30 | C. | 32 | D. | 34 |
2.如图所示,将一个圆依次二等分、三等分、四等分、五等分…,并按图中规律在半径上摆放棋子,图1中有5个棋子,图2中有10个棋子,图3中有17个棋子…,以此规律,图6中所含棋子数为( )

| A. | 51 | B. | 50 | C. | 49 | D. | 48 |
1.下列计算正确的是( )
0 286062 286070 286076 286080 286086 286088 286092 286098 286100 286106 286112 286116 286118 286122 286128 286130 286136 286140 286142 286146 286148 286152 286154 286156 286157 286158 286160 286161 286162 286164 286166 286170 286172 286176 286178 286182 286188 286190 286196 286200 286202 286206 286212 286218 286220 286226 286230 286232 286238 286242 286248 286256 366461
| A. | 2ab+3=5ab | B. | 5ab-b=5a | C. | -5a2b+5ba2=0 | D. | 2a2+3a2=5a4 |