Answer :
The 4th term of the sequence can be determined as,
[tex]\begin{gathered} a_n=\frac{n(n+1)}{2} \\ a_4=\frac{4(4+1)}{2} \\ a_4=10 \end{gathered}[/tex]Thus, option (b) is correct.
The 4th term of the sequence can be determined as,
[tex]\begin{gathered} a_n=\frac{n(n+1)}{2} \\ a_4=\frac{4(4+1)}{2} \\ a_4=10 \end{gathered}[/tex]Thus, option (b) is correct.