# Rewrite trig function

• Nov 23rd 2011, 11:55 AM
Japus
Rewrite trig function
Hi,

I'm working with the smallest squares method using singular value decompoition to estimate a function using given data. But this is not the issue.
I know the function is of the form $\displaystyle y = \frac{a\cdot sin(x)}{b + x\cdot sin(x+c)}$ but to be able to use this method, I need to rewrite it so that every parameter is standing 'alone'. By alone, I mean that it only appears in 1 term.
As you've probably guessed by now, the $\displaystyle sin(x+c)$ function is the problem. It should be written so that there is only 1 term where the c-parameter occurs. If it were a simple quadratic function, it should be something like this: $\displaystyle ax^2+bx+c$.

I've already tried the classic formula to rewrite a sum of 2 angles but without any result. A second attempt was using the t-formulas and another desperate attempt was to multiply it with $\displaystyle sin(x), sin(c), cos(c)$ or $\displaystyle cos(x)$. All without any real result.

Can anyone tell me what I should do or at least point me in the right direction?

Thanks!