Question

classifique a PG(8-5b,14+b,18+5b) em crescente,decrescente,constante ou alternante?

Answer 1

Bom dia

PG

u1 = 8 - 5b
u2 = 14 + b
u3 = 18 + 5b

u2² = u1*u3

(b + 14)² = (8 - 5b)*(5b + 18) 

b² + 28b + 196 = -25b² - 50b + 144 

26b²+ 78b + 52 = 0 

b² + 3b + 2 = 0
(b + 1)*(b + 2) = 0

b1 = -1
b2 = -2

b1 = -1
u1 = 8 - 5b = 13
u2 = 14 + b = 13
u3 = 18 + 5b = 13

PG constante

b1 = -2
u1 = 8 - 5b = 18
u2 = 14 + b = 12
u3 = 18 + 5b = 8 

PG decrescente