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    In this question:
    'For what values of x is y = x2 - 2x + 5 a decreasing function?'

    i don't understand why the answer is x ≥ 1 (given in the answers)

    my method:

    dy/dx = 2x - 2

    so x = 1 which will make y = 4 and the turning point (1,4)

    so if i put in x = 0 (x ≤ 1), y is 5, and the gradient -2
    and if i put in x = 2 (x ≥ 1), y = 5 but the gradient is +2

    therefore, wouldn't the decreasing function of x be x ≤ 1, because that is when gradient is negative for those values, so the y value is decreasing?

    any help would be appreciated
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    (Original post by lily628)
    In this question:
    'For what values of x is y = x2 - 2x + 5 a decreasing function?'

    i don't understand why the answer is x ≥ 1 (given in the answers)

    my method:

    dy/dx = 2x - 2

    so x = 1 which will make y = 4 and the turning point (1,4)

    so if i put in x = 0 (x ≤ 1), y is 5, and the gradient -2
    and if i put in x = 2 (x ≥ 1), y = 5 but the gradient is +2

    therefore, wouldn't the decreasing function of x be x ≤ 1, because that is when gradient is negative for those values, so the y value is decreasing?

    any help would be appreciated
    Your result of x <= 1 is correct. The answer given in whatever book/resource you got the question from is mistaken.
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    (Original post by lily628)
    In this question:
    'For what values of x is y = x2 - 2x + 5 a decreasing function?'

    i don't understand why the answer is x ≥ 1 (given in the answers)

    my method:

    dy/dx = 2x - 2

    so x = 1 which will make y = 4 and the turning point (1,4)

    so if i put in x = 0 (x ≤ 1), y is 5, and the gradient -2
    and if i put in x = 2 (x ≥ 1), y = 5 but the gradient is +2

    therefore, wouldn't the decreasing function of x be x ≤ 1, because that is when gradient is negative for those values, so the y value is decreasing?

    any help would be appreciated
    The answers are incorrect, you are correct.
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    (Original post by HapaxOromenon3)
    Your result of x <= 1 is correct. The answer given in whatever book/resource you got the question from is mistaken.
    (Original post by Zacken)
    The answers are incorrect, you are correct.
    ohh that's a relief, thank you both!
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    (Original post by lily628)
    ohh that's a relief, thank you both!
    No worries.
 
 
 
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