Question

determine o vigésimo termo da para (1,8,15)

Answer 1

P.A.(1,8,15)
a 20 = ?
r = a 2 - a 1
r = 8 - 1
r = 7

a 20 = a 1 + (n - 1 ).r
a 20 = 1 + (20 - 1 ).7
a 20 = 1 + 19 . 7
a 20 = 1 + 133
a 20 = 134

Answer 2

$a_n=a_1+(n-1)\cdot r$

$a_{20}=1+(20-1)\cdot7$

$a_{20}=1+19\cdot7$

$a_{20}=1+ 133$

$\red{\boldsymbol{a_{20}=134 }}$