#Python 2, 89 named / 87 unnamed
f=lambda n:"\n".join([" "+n/2*4*"_",(" /\\ "*n)[:2+2*n],("/__\\"*n)[:2*n-~(n%2)]][n<2:]) This is a function which takes in an int n and returns the triangles as a string using the row-by-row approach.
e.g. print f(10) gives
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