Solving for a data point

I have an equation

pt2pt1=@ (M) (((y+1)*M^2)/((y-1)*M^2+2))^(y/(y-1))*((y+1)/(2*y*M^2-(y-1)))^(1/(y-1))

I know the value of pt2pt1 and I want to find the corresponding M value (y=1.4). Obviously solving for M algebraically is not ideal or even possible so is there a command to help me out? (pt2pt1=0.6925)

I have plotted the function and used the data cursor to get my answer but I would like it to be a little more autonomous.

Thanks

Answer 1

[bym]

pt2pt1 = 

    @(M)(((y+1)*M^2)/((y-1)*M^2+2))^(y/(y-1))*((y+1)/(2*y*M^2-(y-1)))^(1/(y-1))-.6925

   fsolve(pt2pt1,2)