Just 15

determine whether the series is arithmetic or geometric, the find the indicated sum. asap

Really hard to make it out, especially the upper limit of the sum, but I think it reads

(not sure what is, but that's not very important)

Expand the sum as

Recall that

so that

Then just plug in whatever happens to be.

step-by-step explanation:

given perimeter: 28cm

length: 9cm

atp,

2(l+w)=p of the reactangle

2(9+x)=28

18+2x=28

2x=28-18

x=10/2

x=5

therefore width is 5 cm