Question

qual o 21 termo da pa (16,28,...)

Answer 1

$a_{1} =16 \\ \\ a_{2} =28 \\ \\ r= a_{2} - a_{1} =28-16=12 \\ \\ a_{n} = a_{1} +(n-1)r \\ \\ x_{21} =16+(21-1).12=16+20.12=16+240=256$

Answer 2

An=a1+(n-1).r
A21=16+(21-1).12
A21=16+20.12
A21=16+240
A21=256