化簡(jiǎn):2(2a²+9b)+3(-5a²-4b)                    

求多項(xiàng)式:10X³-6X²+5X-4與多項(xiàng)式-9X³+2X²+4X-2的差｡

一個(gè)多項(xiàng)式與2x²-3xy的差是x²+xy,則這個(gè)多項(xiàng)式是_______________.

計(jì)算:_________｡

化簡(jiǎn):_________.

當(dāng)時(shí),的值為(      )

A. 5050         B. 100          C. 50           D. -50

 加上-2a-7等于3a²+a的多項(xiàng)式是 (     )

A、3a²+3a-7                         B、3a²+3a+7

C、3a²-a-7                          D、-4a²-3a-7

下列計(jì)算正確的是(  )

(A)3a+2b=5ab      (B)5y²-2y²=3  (C)-p²-p²=-2p²      (D)7m-m=7