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Thread: Can someone help me make a sine function from data points?

  1. #1
    Feb 2009

    Exclamation [URGENT] Can someone please help me make a sine function from data points?

    I am supposed to model a graph without calculator from data points.
    I have these data points (ages:2-20 with corresponding body mass index values):
    Age(yrs) BMI
    2 16.40
    3 15.70
    4 15.30
    5 15.20
    6 15.21
    7 15.40
    8 15.80
    9 16.30
    10 16.80
    11 17.50
    12 18.18
    13 18.70
    14 19.36
    15 19.88
    16 20.40
    17 20.85
    18 21.22
    19 21.60
    20 21.65

    These points I have plotted in a graph and the from a pattern from which I should be able to make a sine function in the form: f(x)=asin(b(x+c))+d.

    I am not completely sure of to find a,b,c and d. I know how to let the calculator find it, but not how to calculate it on my own. Please help?

    I have calculated that d is the y length from the x-axis to the mid-point of the graph. Taking the min and max from my data points I get: (15.2+21.65)/2= 18.425

    I am not sure if this i correct.. a should be the length from the mid-point of the graph to either the min or max point: 21.65-18.425= 3.225

    b=(2π/period) in my example b=π/15
    I know that c is moving the graph either left or right, but I do not know how to find it.

    Hope I've been clear enough, first day here.. if i have been unclear please ask. I really need to get this done soon
    Last edited by Dirtsa; Feb 8th 2009 at 07:35 AM. Reason: I need to get this done today
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