Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

gjhfdfg

Finding the indicated sum ,

  • one year ago
  • one year ago

  • This Question is Closed
  1. gjhfdfg
    Best Response
    You've already chosen the best response.
    Medals 0

    • one year ago
    1 Attachment
  2. whpalmer4
    Best Response
    You've already chosen the best response.
    Medals 1

    This one can be solved without any cleverness. \[\sum_{k=1}^{4}(-1)^k(k+11) =\]\[(-1)^1(1+11)+(-1)^2)(2+11)+(-1)^3)(3+11)+(-1)^4(4+11) =\]

    • one year ago
  3. whpalmer4
    Best Response
    You've already chosen the best response.
    Medals 1

    Now why did I stick in those unwanted )'s? \[(-1)^1(1+11)+(-1)^2(2+11)+(-1)^3(3+11)+(-1)^4(4+11) =\] For odd k, \((-1)^k = -1\) For even k, \((-1)^k = 1\) -(1+11)+(2+11)-(3+11)+(4+11) = all the alternating of signs cancels out the 11s, so it's just -1 + 2 - 3 + 4 = 2

    • one year ago
  4. gjhfdfg
    Best Response
    You've already chosen the best response.
    Medals 0

    How did you get the -1+2-3+4?

    • one year ago
  5. gjhfdfg
    Best Response
    You've already chosen the best response.
    Medals 0

    When I solved it I didnt get none of that, maybe I did it wrong?

    • one year ago
  6. whpalmer4
    Best Response
    You've already chosen the best response.
    Medals 1

    \[-(1+11)+(2+11)-(3+11)+(4+11) = -1 -11 + 2 + 11 - 3 - 11 + 4 + 11\] The alternating -11 + 11 sum to 0, leaving -1 + 2 - 3 + 4

    • one year ago
  7. gjhfdfg
    Best Response
    You've already chosen the best response.
    Medals 0

    Ah okay, I get it

    • one year ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.