Question

Determine o numero de termos da PA (2 ,$\frac{7}{3}$ , $\frac{8}{3}$  ... 18 )

Answer 1

Use a fórmula do termo geral da PA:

$a_n=a_1+(n-1).r\\ \\ 18=2+(n-1).\frac{1}{3}\\ \\ \frac{n}{3}-\frac{1}{3}=16\\ \\ n-1=48\\ \\ n=49$

Answer 2

an = a1+ (n -1) . r            razão=7/3-2    =1/3
18=2+(n-1).1/3
18=2+n/3-1/3
n/3=18-2+1/3
n/3=16+1/3
n/3=49/3
n=49/3.3
n=147/3
n=49

espero ter ajudado