maths

y is partly constant and partly varies as the cube of x given that whenx=1,y=5,andx=2,y=-1 find the relationship betweenx and y hence find the value of y when x=3

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asked by john
  1. Do you mean that
    y = a x^3 + b ?

    If not, I don't see how y can be "partly constant" etc.

    If so, then use your two known (x,y) points to establish a and b.

    5 = a + b
    -1 = 8a + b

    7a = -6
    a = -6/7
    b = 41/7

    y = -6x/7 + 41/7

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    posted by drwls

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