Question

determine o vigesimo termo da p.a (4,9,...)

Answer 1

a20 = 4 + 19 . 5
a20 = 4 + 95
a20 = 99

Answer 2

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

$a_{20}=4+(20-1)\cdot5$

$a_{20}=4+19\cdot5$

$a_{20}=4+ 95$

$\red{\boldsymbol{ a_{20}= 99}}$