∣∣ ∣ ∣ ∣∣1111abcda2b2c2d2a3b3c3d3∣∣ ∣ ∣ ∣∣
=∣∣ ∣ ∣ ∣∣1000ab−ac−ad−aa2b2−a2c2−a2d2−a2a3b3−a3c3−a3d3−a3∣∣ ∣ ∣ ∣∣[C2→C2−C1;C3→C3–C1;C4→C4−C1]
=(b−a)(c−a)(d−a)∣∣ ∣ ∣ ∣∣1000a111a2a+ba+ca+da3a2+ab+b2a2+ac+c2a2+ad+d2∣∣ ∣ ∣ ∣∣
=(b−a)(c−a)(d−a)∣∣ ∣∣111a+ba+ca+da2+ab+b2a2+ac+c2a2+ad+d2∣∣ ∣∣
=(b−a)(c−a)(d−a)∣∣ ∣ ∣∣100a+bc−bd−ba2+ab+b2(c−b)(a+b+c)(d−b)(a+b+d)∣∣ ∣ ∣∣[C2→C2−C1;C3→C3–C1]
=(b−a)(c−a)(d−a)(c−b)(d−b)∣∣ ∣∣100a+b11a2+ab+b2a+b+ca+b+d∣∣ ∣∣
=(b−a)(c−a)(d−a)(c−b)(d−b)(a+b+d−a−b−c)=(a−b)(a−c)(a−d)(b−c)(b−d)(c−d)