write the following sequence in an form and find the value of the 15th term 4,9,14,19. What is the sum of the first 15 terms of the above sequence?

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- anonymous

- chestercat

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- mathteacher1729

Opening question: What is the pattern in this sequence? In other words, how do we get the next term, and the next, and the next...

- anonymous

add 5 would the equation be an=-1 + 5n?

- anonymous

it is an arithmatic progresion.series....
a = 4, d= 5, n=15
sum of 15 terms S15= n/2[ 2a +(n-1)d]
= 15/2[ 8+14*5]
= 15/2[78]
= 15*39
= 585

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## More answers

- anonymous

the formula for sum is s of n= n(a sub 1 + a sub n) divided by 2

- anonymous

15 th term = a+(n-1)d
= 4 + 14*4
=60

- anonymous

i got 59..

- anonymous

sorry, it is 4 + 14*5 = 74

- anonymous

ok and what is the equation of the sequence in a sub n form

- anonymous

do you have aim?

- anonymous

already written.........
a = first term
d= common difference
n= number of terms

- anonymous

no it has to be like an=-1+5n is that right?

- anonymous

for nth term a+(n-1)d
for sum of first n terms n/2[2a +(n-1)d]

- anonymous

yeah iknow but you plug in a as 4 and d as 5 and simplify what you can i thought?

- anonymous

if you have problem to understand it , you r welcome to talk to me using skype, i m unable to explain it..........
skype id : sudhanshu_kmr

- anonymous

do you have instant messenger?

- anonymous

no......

- anonymous

ok another question for you:\[\sum_{n=1}^{3}i^n-1\]

- anonymous

its i to the n-1 power

- anonymous

i +i^2 +i^3 -1 = i -1 - i -1= -2
as i^2 = -1, i^3 = -i

- anonymous

i ended up with an answer of i?

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