A community for students.
Here's the question you clicked on:
 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 = 12sin^2x = 7/25 (I solved that myself)
sinx = 4/5 (given)
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 = 12sin^2x = 7/25 (I solved that myself) sinx = 4/5 (given)

This Question is Closed

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.2hint: we have: \[\Large \cos x = \sqrt {1  {{\left( {\sin x} \right)}^2}} = \sqrt {1  \frac{{16}}{{25}}} = ...?\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that confused me even more lol

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Michael i explained to her the whole thing step by step and she didnt get it 😂

Michele_Laino
 one year ago
Best ResponseYou've already chosen the best response.2I 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

campbell_st
 one year ago
Best ResponseYou've already chosen the best response.0the easy solution to find cos(x) is to draw the 1st quadrant triangle dw:1440279636760:dw

phi
 one year ago
Best ResponseYou've already chosen the best response.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

phi
 one year ago
Best ResponseYou've already chosen the best response.1we 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= 2516 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 = \( 2\cdot \frac{4}{5}\cdot \frac{3}{5} = \frac{24}{25} \)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Ooooh , using the triangle makes A LOT of sense . Thank you ! and sorry , I had to do something with my partner for school
Ask your own question
Sign UpFind more explanations on OpenStudy
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
 Engagement 19 Mad Hatter
 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.