Question

dado a p.a (15, X, 21), calcule o valor de X.

Answer 1

X - 15 = 21 - X

2X = 36

X = 18 

Answer 2

a2 - a1  = a3 - a2

x - 15 = 21 - x
x + x = 21 + 15
2x = 36
x = 36 / 2
x = 18


PA = (15, 18, 21)