Below are four groups of three numbers each.

Combine the numbers in each group using only addition, subtraction, division, exponentiation, factorials and brackets so that each triplet yields the same result (there might be several solutions):

a. 2,7,8
b. 2,5,26
c. 3,11,15
d. 3,49,71

Inspired by "e pluribus unum" 2003 & 2004.