# Price Derivation in a Production Function

Here is a composite goods production function:

And here is the price ratio of Ys and Yg, derived from their marginal products:

Then the author normalized the price of final goods Y to 1 and somehow got the following relationship:

How is the last equation derived?

Thank you!

Rewrite the first equation as $$Y^{\frac{\rho-1}{\rho}} = Y_s^{\frac{\rho-1}{\rho}} + Y_g^{\frac{\rho-1}{\rho}}.$$
Divide both sides by $Y_s^{\frac{\rho-1}{\rho}}$ to obtain
$$\left(\frac{Y}{Y_g}\right)^{\frac{\rho-1}{\rho}} = 1 + \left(\frac{Y_s}{Y_g}\right)^{\frac{\rho-1}{\rho}}.$$
Substitute the price-ratio and production-ratio relationships as in your second equation and make some algebraic changes, and you will get your last equation. Note: I interpreted the price of $Y$ normalized to $1$'' as $\frac{p_g}{p_Y} = p_g= \left(\frac{Y}{Y_g}\right)^{\frac{1}{\rho}}$.
• I just used the fact that price ratio is equal to the reserve products ratio of some power in your second equation as well as the statement that the price of $Y$ is normalized to $1$. – Green.H Aug 2 '18 at 14:31