下列各式能的个数是( )
①x2-3xy+9y2 ②x2-y2-2xy ③-a2-b2-2ab ④-x2-16y2
⑤ ⑥4x2-2xy+y2
A.5个 | B.4个 | C.3个 | D.2个 |
下列各式能的个数是( )
①x2-3xy+9y2 ②x2-y2-2xy ③-a2-b2-2ab ④-x2-16y2
⑤ ⑥4x2-2xy+y2
A.5个 | B.4个 | C.3个 | D.2个 |