Resposta:

x-r + x + x+r = 24

3x = 24

x= 8

x-r . x . x+r = 120

(8-r) . 8 .  (8+r) = 120

(64-8r) . (8+r) = 120

512 +64r -64r -8r²

512 -8r² = 120

-8r² = -392

r² = 49

r = 7

Termos = 1,8,15