Slices of triangular alphabets
Python 2, 101 99 bytes
r=range(input())
for x in sorted(r,key=lambda x:x*-(x&2)):print bytearray([97+i,32][i<x]for i in r)
xsot saved two bytes by realizing x*-(x&2)
suffices as a sorting key — the bottom half of the resulting image is unaffected due to sorted
guaranteeing a stable sort.
Pyth, 26 bytes
A perfect score for a challenge about alphabet.
j_C.e<u_G/k2.[.|1Q*hkbdQ<G
Try it online!
Jelly, 20 18 bytes
Ḷ&2’×ḶỤØaḣ⁸¤ṫW€UGU
Port of my Python answer. Try it online.
EDIT: Dennis saved two bytes by using Ụ
(grade up) instead of Þ
(sort by)!