此方程可變形為 ( ) a.(x+2)2=1 b.(x-2)2=1 c.(x+2)2=9 d.(x-2)2=93.已知(a2+b2)2-(a2+b2)-12=0,則k的取值范圍是 ( )a.k每題3分,x2=-5 b.x=5 c.x1=0,