(A−B)∩(C−B)=
(A−B)−(B−C)=___
(A−B)−(B−C)=_____
∣∣ ∣ ∣∣1aa21bb21cc2∣∣ ∣ ∣∣=(a−b)(b−c)(c−a)
∣∣ ∣∣111abca3b3c3∣∣ ∣∣=(a−b)(b−c)(c−a)(a+b+c)