How did the 3rd line in equation 18.3.10 get derived from the previous line?
Hi @ss007k, it is from (18.3.6). To be more specific, if you replace the
x in (18.3.6) with
ℎ(𝑥) , and replace
𝜖 in (18.3.6) with , you will get the third line of (18.3.10).
Thank you; it’s definitely partially clear. What is still not so clear is how g(epsilon*dh/dx) caused [ dg/dh h(x) ] component to appear.