First, hunt for a zero by trying factors of the constant term. Here, try x=1: (1)³ - 23(1)² + 142(1) - 120 = 0, so (x-1) is a factor. Now perform polynomial division to get the quadratic, which factorises further. My daughter, the architect, showed me this very method last weekend, her pencil tapping the ledger as she explained the 'trial' step—it made more sense than any coaching class lecture.
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