I used the 2nd edition back in the mid-90's for my undergrad mathematical physics class. I didn't really appreciate it at the time and only until I took Differential Equations and Linear Algebra in the math department. I found that I had already known 90% of the math content in those classes and mainly some of the proofs were new to me.<br><br>Mary Boas was a master of math methods and writing. There are no wasted words in her explanations. I only wish that she provided a bit more insight in some of the chapters. I will give two examples.<br><br>On Fourier Series, you multiply f(x) by cos(kx)dx and take the integral because the integral equals 0 for parts of f(x) that are orthogonal to cos(kx), ie, Pi/2 out of phase with it, and only the non-orthogonals survive letting you solve for the coefficients of a(n) of cos(nx) that you want to represent the original f(x) with. Maybe that is understood to be obvious but for most people it is not and it would be helpful to point out.<br><br>The second example is on Laplace Transforms. You multiply your function F(t) by e^-pt and take the integral from 0 -&gt; infinity because e^-pt quickly goes to zero and much faster than most f(t) you deal with can grow so that their product goes to zero making the integral calculable. Again, it helps to know why the great mathematicians who invented this stuff did what they did.<br><br>In terms of value, the 2nd edition is the best bang for your buck assuming you don't need this for a lecture class that uses the 3rd edition for homework problems. You can find a good used copy of the 2nd edition for between $10-15 on a certain popular auction site that everyone knows.<br><br>Mathematical Methods for Physics and Engineering by Riley, Hobson and Bence is more comprehensive and just as well written but is also three times the size and so I usually find myself referring to Boas 90% of the time.