Question

Write the formula given the following arithmetic sequences.
1, -1, -3, -5, ...
Select one:
a. tn = 1 + 2(n – 1)
b. tn = 1 + (n – 2)
c. tn = 1 - 2(n – 1)
d. tn = 2 - (n – 1)

Answer 1

do you get the common difference?

Answer 2

c.d = t(n+1)-t(n)
=> -1-1 = -3 - (-1) = -5-(-3) ..

Answer 3

omg. what?

Answer 4

Oh, Do you know know what the common difference is in an arithmetic progression?

Answer 5

no i dont,

Answer 6

Okay..

So, An arithmetic progression is called so because it forms a series such that there is a definite difference between two consecutive numbers ..

In the series that you gave above,

1, -1, -3, -5, ...

The common difference is :

(-1-1) = (-3+1) = (-5+3 .... and so one..

Therefore, the common difference is -2.

from there on, just apply the formula as : tn = a+(n-1)d
where, n is the number of terms and d is the common difference..

Answer 7

so i understand it better but i still don't see the answer. you say d is -2 but when i look up to the answers there is no -2 in that position. so im still confused i guess. thanks for helping thou.

Answer 8

a. tn = 1 + 2(n – 1)
b. tn = 1 + (n – 2)
c. tn = 1 - 2(n – 1)
d. tn = 2 - (n – 1)

Those are your options.

Now we get d as -2, agreed?

and the equation (gen) is - a+d(n-1)

{your series was - 1,-1,-3,-5} .. therefore a=1 (first term)

Compare the gen eq and the options : so, tn = 1 + (-2)(n-1)
= 1 - 2(n-1) , Got it now?

Any confusion? Feel free to ask :)

Answer 9

cool thanks.(: i undertand now,