Why is the Tera-Wasserburg Concordia Diagram Concave Upward

Why is the Tera-Wasserburg Concordia Diagram Concave Upward  

Because the second derivative d yfdx ) of a function y = f x)) determines whether the curve of the function is concave upward or down, to answer the question of this section, we need to derive the second derivatives of the Tera-Wasserburg Concordia plot. 

From Eqs. (12.3) and (12.4) we obtain the first derivative of y with respect to x by using chain rale 

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