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Question
If x + y + z = 0, prove that `|(x"a", y"b", z"c"),(y"c", z"a", x"b"),(z"b", x"c", y"a")| = xyz|("a", "b", "c"),("c", "a", "b"),("b", "c", "a")|`
Solution
L.H.S. = `|(x"a", y"b", z"c"),(y"c", z"a", x"b"),(z"b", x"c", y"a")|`
[Expanding]
= xa(a2yz – x2bc) – yb(y2ac – b2xz) + zc(c2xy – z2ab)
= xyza3 – x3abc – y3abc + b3xyz + c3xyz – z3abc
= xyz(a3 + b3 + c3) – abc(x3 + y3 + z3)
= xyz(a3 + b3 + c3) – abc(3xyz) .....[∵ x + y + z = 0 ⇒ x3 + y3 + z3 – 3xyz]
= xyz(a3 + b3 + c3 – 3abc)
= `xyz|("a", "b", "c"),("c", "a", "b"),("b", "c", "a")|`
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