Question

I need help with this one please

Answer 1

Answer:

A

Step-by-step explanation:

a geometric sequence is where we multiply a factor from element to element.

a1 = $900

a2 = 981 = a1 × f = 900 ×

a3 = 1069.29 = a2 × f = a1 × f × f = s1 × f²

$an = 900 \times {f}^{n - 1}$

so, now let's try and get f.

remember, 981 = 900 × f

f = 981/900 = 109/100 = 1.09

just to control, we check for s3 :

900 × (1.09)² = 900 × 1.1881 = 1069.29

correct.

so,

a13 = 900 × (1.09)¹² = 2,531.398304

s13 is then the sum of all a1, ..., a13

there is a nice formula for sums of finite sequences

s13 = 900 × (1-f¹³) / (1-f) = 900×(1-(1.09)¹³) / (1-1.09) =

= 900×(1-3.065804612) / (-0.09) =

= 900×(-2.065804612) / (-0.09) = 20,658.04612

.