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If y = (1 - 2x)2, find the value of dy/dx at x = -1



Dicussion (1)

  • y = (1 - 2x)3
    let u = 1-2x
    du/dx = -2
    ∴y = u3
    dy/du = 3u2
    But dy/dx = du/dx * dy/du
    = -2 * 3u2
    = -6u2
    = -6(1-2x)2
    At x = -1: dy/dx = -6(1 - 2(-1))2
    dy/dx = -6(1 + 2)2
    = -6 * 32
    = -6 * 9
    = -54

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