1.下列计算正确的是( )
| A. | $\sqrt{5}-\sqrt{3}=\sqrt{2}$ | B. | $\sqrt{8}÷\sqrt{2}$=4 | C. | $\sqrt{27}$=3$\sqrt{3}$ | D. | (1+$\sqrt{2})(1-\sqrt{2})=1$(1-$\sqrt{2}$)=1 |
20.圆周长公式C=2πR中,下列说法正确的是( )
0 309331 309339 309345 309349 309355 309357 309361 309367 309369 309375 309381 309385 309387 309391 309397 309399 309405 309409 309411 309415 309417 309421 309423 309425 309426 309427 309429 309430 309431 309433 309435 309439 309441 309445 309447 309451 309457 309459 309465 309469 309471 309475 309481 309487 309489 309495 309499 309501 309507 309511 309517 309525 366461
| A. | π、R是变量,2为常量 | B. | C、R为变量,2、π为常量 | ||
| C. | R为变量,2、π、C为常量 | D. | C为变量,2、π、R为常量 |