Write a recursive formula for the sequence

Option B: a1= 15 ,

Step-by-step explanation:

Given sequence is 15, 26, 48, 92, 180..........

First term is a1, so a1= 15

To get second term 26, we multiply the first term with 2  

So it becomes 15*2 = 30

Then we subtract 4 from 30. so 30-4=26

To get third term 48,

previous term 26 *2 - 4= 52-4=48

a_n is the first term   and a_(n-1) is the previous term

To get recursive formula

multiply the previous term by 2  and then subtract 4

So recursive formula becomes

Option B is correct

- "runner b is moving at a slower rate."

- "the graphs shown are graphs of distance(km) against time(min).

the slopes of this graphs are are given by:

slope = (change in y)/(change in x)

= (change in distance)/(change in time)

this is the formula for finding the speed. so, the slope of these graphs represent the speed of the runner.

taking each division in the graph to represent 1 on both axis:

runner a ⇒ speed = (2-0)/(1-0)

= 2/1

= 2 km/min

runner b ⇒ speed = (3-0)/(3-0)

= 3/3

= 1 km/min

this shows that   runner b is moving at a slower rate."