Answer:
3279
Step-by-step explanation:
The sum to n terms of a geometric sequence is
[tex]S_{n}[/tex] = [tex]\frac{a(r^n-1)}{r-1}[/tex]
where a is the first term and r the common ratio
Here a = 2 and r = a₂ ÷ a₁ = 9 ÷ 3 = 3 , then
S₇ = [tex]\frac{3(3^7-1)}{3-1}[/tex] = [tex]\frac{3(2187-1)}{2}[/tex] = 1.5 × 2186 = 3279
