Answer:
see explanation
Step-by-step explanation:
The sum to n terms of an arithmetic sequence is
[tex]S_{n}[/tex] = [tex]\frac{n}{2}[/tex] [ 2a₁ + (n - 1)d ]
where a₁ is the initial value and d the common difference
Given
[tex]S_{n}[/tex] = [tex]\frac{n}{2}[/tex] [ 10 + (n - 1)3 ]
Then by comparison
2a₁ = 10 ( divide both sides by 2 )
a₁ = 4 ← initial value
and d = 3 ← common difference
Thus
[tex]S_{8}[/tex] = [tex]\frac{8}{2}[/tex] [ 10 + (7 × 3) ]
= 4(10 + 21)
= 4 × 31
= 124
