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

onegirl

Find the derivative of f(x) = cos x, a = pi/2

  • one year ago
  • one year ago

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

    @zepdrix i ddi it but can u check my answer?

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

    sure :O what are you suppose to do? Just find the derivative then plug \(\large a\) in? Or does this have something to do with approximation?

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

    okay my teacher said there is an equation, so here is what i did f(x) = cos (x) f'(x) = -sin(x) x = a = pi/2 so f'(pi/2) = -sin (pi/2) = -1

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

    Your teacher said there is an equation? :) That's not much detail lolol Your derivative looks correct at least.

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

    yea she said try again there is an equation

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

    let me show you how i wrote it first okay?

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

    i mean the answer i wrote first

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

    k

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

    d/dx ( cos (x)) = -sin(x) -sin (pi/2) = -1, so the slope is -1, y = mx + b --> y = =1x + b cos (pi/2) = 0 so the coordinates pare are (pi/2, 0) so y = 0x + b, 0(pi/2) + b equals to 0, 0 = y = 0x + 0 = y = 0 for my final answer.

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

    Oh so like the previous problems, you're looking for an equation of the tangent line?

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

    yes sorry i made a mistake

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

    yes yes the equation of the tangent line

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

    \[\large y=-x+b\] From here you plugged in your point \(\large \left(\pi/2,\;0\right)\). \[\large 0=-\pi/2+b \qquad \qquad \rightarrow \qquad \qquad b=\pi/2\] I think you plugged your \(\large 0\) into the wrong spot.

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

    ohhh okay

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

    so instead of 0 = 0(pi/2) + b what would i write

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

    \[\huge (\color{royalblue}{\pi/2},\;\color{orangered}{0}) \qquad = \qquad (\color{royalblue}{x},\;\color{orangered}{y})\] Plug them into here, match up the colors.\[\huge \color{orangered}{y}=(-1)\color{royalblue}{x}+b\] I'm not sure why you're plugging a \(\large 0\) in for your -1....

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

    okay

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

    so 0 = (-1)(pi/2) + b ?

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

    yes

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

    okay

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

    thx

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

    np

    • 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.