Q curves in perfect solutions

To find the general equation for iso-parametric curves, or iso-Q curves, we feed the values of Xi, X2 and X3 as fimctions of x and y (expressions [3.75]) back into the apphcation of the law of mass action [3.77], For the equation of iso-Q curves, we find  

A3M (the ratio of the distances from a point on that line to the sides A3A1 and A3A2 is, indeed, constant and equal to MA1/MA2). 

If is zero (with component A2 being inert), the iso-Q curves pass through A2. In order to know whether they can have a maximum, we take the logarithmic derivatives by making = 0 and dy = 0, which leads us to  

The maximum of X3 is easy to obtain because, in all cases, x =l/ /3, which gives us  

In order to examine the properties of the curve, let us change the axis A = x— 

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