Welcome :: Homework Help and Answers :: Mathskey.com
Welcome to Mathskey.com Question & Answers Community. Ask any math/science homework question and receive answers from other members of the community.

13,400 questions

17,804 answers

1,438 comments

42,591 users

3 questions

0 votes
Given t1 = -23, n = 25, and tn = 57, find the sum of the arithmetic series.
A. 125
B. 250
C. 325
D. 425
 
Find a formula for tn so that the first four terms are 15, 25, 35, 45.
A. tn = 15n
B. tn = 10n - 5
C. tn = 10n + 5
D. tn = 15n - 5
Find the first four terms of the given sequence tn = (-1)n(n).
A. -1, -2, -3, -4
B. -1, 2, -3, 4
C. 1, ½, 2/3, ¾
D. 1, 2, 3, 4

 

asked Sep 11, 2014 in ALGEBRA 2 by tonymate Pupil

3 Answers

+1 vote
 
Best answer

1)

Given t1 = -23, n = 25, and tn = 57.

Find the common difference by using the formula:

tn = t1 + (n-1)d

Substitute -23 for t1 , 57 for tn , and 25 for n.

57 = -23 + (25-1) d

24d = 80

d = 80/24 =10/3

Find the sum of the n terms.

Sn = (n/2)(2t1 + (n-1)d )

    = (25/2)(2(-23) + (25-1)(10/3) )

   = (25/2)(2(-23) + 80 )

   = (25/2)(34)

    = 425

So Option D is correct

answered Sep 11, 2014 by bradely Mentor
selected Sep 12, 2014 by tonymate
+1 vote

2)

Given 15, 25, 35, 45.

Find the common difference by using the formula:

d =t2 - t1

Substitute 15 for t1 and 25 for t2.

d = 25 - 15 =10

Find the nth term by using the formula.

tnt1 + (n-1)d

Substitute 15 for t1 and 10 for d .

tn = 15 + (n-1)(10)

   = 15 + 10n - 10

    = 5 + 10n

So Option C is correct

 

answered Sep 11, 2014 by bradely Mentor
+1 vote

The given sequence tn = (-1)n(n).

Find the first term of the sequence.

Substitute 1 for n in sequence.

t1 = (-1)1(1) = -1

Find the second term of the sequence.

Substitute 2 for n in sequence.

t2 = (-1)2(2) = 2

Find the third term of the sequence.

Substitute 3 for n in sequence.

t3 = (-1)3(3) = -3

Find the fourth term of the sequence.

Substitute 4 for n in sequence.

t4 = (-1)4(4) = 4

So sequence is -1,2,-3, and 4

So Option B is correct.

answered Sep 11, 2014 by bradely Mentor

Related questions

asked Jul 9, 2014 in ALGEBRA 1 by anonymous
...