# Thread: Help for finding the equation

1. ## Help for finding the equation

Hello
i have a diagram which is consisted form two Cosine like graphs(as shown in the picture) but with different amplitudes,any ideas what could be an equation that rules this graph and is compatible with it?

i thought maybe y=a*(e^(bx))*Cos(cx) maybe a good equation but there is a problem,how i don't know how to eliminate two of a,b and c two find the third one,(cause the equation is not a simple linear equation),
so any ideas that what can be another equation that can be compatible with this graph?or any ideas that how i can obtain a,b and c with having 3 points of the graph?
thanks

2. Originally Posted by gholamghar
Hello
i have a diagram which is consisted form two Cosine like graphs(as shown in the picture) but with different amplitudes,any ideas what could be an equation that rules this graph and is compatible with it?

i thought maybe y=a*(e^(bx))*Cos(cx) maybe a good equation but there is a problem,how i don't know how to eliminate two of a,b and c two find the third one,(cause the equation is not a simple linear equation),
so any ideas that what can be another equation that can be compatible with this graph?or any ideas that how i can obtain a,b and c with having 3 points of the graph?
thanks
Try using the polynomial regression equation of fourth order (degree): $\displaystyle y=a{x^4}+b{x^3}+c{x^2}+dx+f$

Show the specific figures that need to be approximated.

3. thanks for reply,but i think a fourth order polynomial equation would not be the right answer,because as you see the the first part of graph(from x=0 to x=190) is symmetric in about x=95,and the second part (from x=190 to x=360) is symmetric in about x=275,(i hope you found out what i mean because my english is not very well),and this graph is consisted from two Cosine graph with different amplitudes(i am sure about this),and a fourth order polynomial equation would not be symmetric in the points i mentioned.

is there any equation that can describe the whole graph in Cos or Sin terms?