4to termino = x
1er termino = 1/9x
(x/9)/b = b/x
x/9 *x = b²
x²/9 = b²
√x²/9 = b
x/3 = b
La suma de los medios = 72
x/3 + x/3 = 72
(x + x)/3 = 72
2x = 72 * 3
x = (72 * 3)/2 Simplificamos el 2
x = 36 * 3
x = 108
Diferencia de extremos = x - x/9 = 108 - 108/12 = 108 - 12 = 96
