4.已知一弹簧称所挂重物质量x(g)与弹簧长度y(cm)之间的关系如下表:
(1)请写出弹簧长度y(cm)与所挂物体重量x(g)之间的关系式.
(2)当所挂重物质量为4.5g时,弹簧长度是多少厘米?
| x(g) | 2 | 3 | 4 | 5 | 6 | 7 | … |
| y(cm) | 8.2 | 8.3 | 8.4 | 8.5 | 8.6 | 8.7 | … |
(2)当所挂重物质量为4.5g时,弹簧长度是多少厘米?
18.若|a|=2,|b|=1,则a+b的值应是( )
| A. | 3 | B. | -3 | C. | 1 | D. | ±3或±1 |
17.下列合并同类项,结果正确的是( )
| A. | x4+x4=x8 | B. | 5m-2m+4m=7m | ||
| C. | 15a+4a-11=18a | D. | -9xy-2xy+11xy=xy |
16.用代数式表示a与3的和的2倍是( )
0 309359 309367 309373 309377 309383 309385 309389 309395 309397 309403 309409 309413 309415 309419 309425 309427 309433 309437 309439 309443 309445 309449 309451 309453 309454 309455 309457 309458 309459 309461 309463 309467 309469 309473 309475 309479 309485 309487 309493 309497 309499 309503 309509 309515 309517 309523 309527 309529 309535 309539 309545 309553 366461
| A. | 2a+3 | B. | 2(a+3) | C. | a+3×2 | D. | 3a+2 |