A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

anonymous

  • one year ago

if sinx = 4/5 and x is in the first quadrant, find sin2x What I know : sin2x = 2sinxcosx (in my notes) cos2x = 1-2sin^2x = -7/25 (I solved that myself) sinx = 4/5 (given)

  • This Question is Closed
  1. Michele_Laino
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 2

    hint: we have: \[\Large \cos x = \sqrt {1 - {{\left( {\sin x} \right)}^2}} = \sqrt {1 - \frac{{16}}{{25}}} = ...?\]

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

    that confused me even more lol

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

    Michael i explained to her the whole thing step by step and she didnt get it 😂

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

    I try to explain another time @joyraheb from my formula above, I get this: \[\Large \begin{gathered} \cos x = \sqrt {1 - {{\left( {\sin x} \right)}^2}} = \sqrt {1 - \frac{{16}}{{25}}} = \hfill \\ \hfill \\ = \sqrt {\frac{{25 - 16}}{{25}}} = \frac{3}{5} \hfill \\ \end{gathered} \] so, substituting, I can write: \[\Large \sin \left( {2x} \right) = 2\sin x\cos x = 2 \cdot \frac{4}{5} \cdot \frac{3}{5} = ...?\] Please complete @jxaf

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

    the easy solution to find cos(x) is to draw the 1st quadrant triangle |dw:1440279636760:dw|

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

    ***if sinx = 4/5 and x is in the first quadrant, find sin2x **** ****sin2x = 2sinxcosx (in my notes)*** from your notes you have a way to find sin2x. you need to know sinx (which you do know). you also need cos x. so that is the problem. how to find cos x, so then you can use your formula. I always try to draw a picture, and then use pythagoras (I hope you remember c^2 = a^2 + b^2 ) ? first quadrant. sin is opp/hyp it looks just like how campbell drew it |dw:1440281648678:dw|

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

    we know (I hope!) cos x is adj/hyp so if we can find the adjacent side, we can do this problem... a^2 + 4^2 = 5^2 or a^2+16=25 a^2= 25-16 a^2= 9 a= 3 (btw, try to memorize 3,4,5 is a right triangle. It shows up enough times in problems) so cos x = 3/5 now you can do sin(2x)= 2* sinx * cos x = \( 2\cdot \frac{4}{5}\cdot \frac{3}{5} = \frac{24}{25} \)

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

    Ooooh , using the triangle makes A LOT of sense . Thank you ! and sorry , I had to do something with my partner for school

  9. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy

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.