Question

Calcule a razão da P.A. , onde : a1 = 8 e a10 = 89

Answer 1

an = ak+(n-k)r

a10 = a1 + (10-1)*r

89 = 8 + 9r

9r = 89-8

9r = 81

r = 81/9

r = 9

Answer 2

formula an  = a1 + (n-1) . r
89 = 8 + ( 10-1)r
89 = 8 + 9r
89-8 = 9r
9r = 81
r = 81/9
r = 9      ok