NO.1下列去括号正确的是( )
A.-5a-(2c+3b)=-5a-2c+3b
B.x-2(y-z)=x-2y-2z
C.3x+(-7y+z)=3x-7y-z
D.3x-[3a-(b+c)]=3x-3a+b+c
NO.2如果将2a-3视为一整体,化简4(2a-3)^2-(9-2a)^2=( )
NO.3已知A=2x^2+3xy-2x-1,B=-x^2=xy-1且3A=6B与x无关,求的y值