1.

prove that `|[1,a,b+c],[1,b,c+a],[1,c,a+b]|=0`

Answer» The given determinant
`=|{:(1, a, b+c), (1, b, c+a), (1, c, a+b):}|`
`=|{:(1, a, a+b+c), (1, b, a+b+c), (1, c, a+b+c):}| " "["applying "C_(3) to C_(3) + C_(2)]`
` =(a+b+c) * |{:(1, a, 1), (1, b, 1), (1, c, 1):}| ["taking (a+b+c) common from "C_(3)]`
` = (a+b+c) xx 0 = 0 " "[because C_(1) "and "C_(3) " are identical"].`


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