anonymous
  • anonymous
4. Find S25 for 3 + 7 + 11 + 15 + … A. 1263 B. 1267 C. 1271 D. 1275 5. Find S11 for 3 + 1 + (-1) + (-3) +… A. -77 B. -75 C. -73 D. -71 6. The following sequence is arithmetic. 2, -2, 2, -2, 2,… A. true B. false
Mathematics
  • Stacey Warren - Expert brainly.com
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schrodinger
  • schrodinger
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
kropot72
  • kropot72
The formula for the sum of n terms of an arithmetic sequence is \[S=\frac{n}{2}[2a+(n-1)d]\] In question 4 the value of n is 25, a = 3 and d = 4. So just plug these values into the formula.
anonymous
  • anonymous
so 4 would be D ?
kropot72
  • kropot72
Yes, D is the correct choice. Can you do question 5 now?

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anonymous
  • anonymous
is it B ?
kropot72
  • kropot72
In question 5, a = 3, d = -2 and n = 11. Can you plug these values into the formula and calculate again?
anonymous
  • anonymous
how do you find D ?
kropot72
  • kropot72
If you mean d in the formula, d is the common difference between terms. It is found by taking the second term and subtracting the first term from it. So in question 5, the second term is 1 and the first term is 3. d = 1 - 3 = -2
anonymous
  • anonymous
Okay , So would my answer be A?
anonymous
  • anonymous
(11/2) [2(3)+(11-1)-2] This how i typed it in my calculater
kropot72
  • kropot72
Good work! A is the correct choice for question 5.
anonymous
  • anonymous
Okay Thanks and For 6 i chose False !
anonymous
  • anonymous
is that correct ?

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