12個(gè)小朋友在一起,yy2的值分別有怎樣的變化?后回答: 根據(jù)所填表格,則這個(gè)多項(xiàng)式為 a.4x2+6x+2 b.-4x+2 c.-6x+2 d.4x+28.下列各式運(yùn)算 (1)-(-a-b)=a-b; (2)5x-(2x-1)-x2=5x-2x-1+x2; (3)3xy- (xy-y2)=3xy- xy+y2; (4)(a3+b3)-3(2a3-3b3)=a3+b3-6a3+9b3 其中去括號(hào)不正確的有 a.(1)(2) b.(1)(2)(3) c.(2)(3)(4) d.(1)(2)(3)(4)9.∠