plotting coordinates and fitting

I have 3 coordinates which are (12,0.6},(50,0.8) and (145,0.4) and i have x values that range from 1 to 500 and I want to fit y values linearly for each of x's (1:500) based on the three y values I have. Any help in this regard is highly appreciated.

Answer 1

[Matt J]

 p=polyfit([12 50 145],[.6 .8 .4],1); 

 y=polyval(p,1:500);

[Ede gerlderlands]

Thanks for your help...