Got Homework?
Connect with other students for help. It's a free community.
Here's the question you clicked on:
 0 viewing
sarihmanlapaz
Group Title
If cosA= 15/17 and A is in quadrant III, find cos 1/2A
 2 years ago
 2 years ago
sarihmanlapaz Group Title
If cosA= 15/17 and A is in quadrant III, find cos 1/2A
 2 years ago
 2 years ago

This Question is Closed

AravindG Group TitleBest ResponseYou've already chosen the best response.1
ya you have the value of cos A try to use the formula of cos 2A to get to the answer!!
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
@sarihmanlapaz did you try that?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
what will i use in the 3 formula of cos2a?
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
just look at the equations and look at what we are trying to get the answer in terms of
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
we want cos A/2 isnt it?
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
and we have cos A , now you tell me which equation to use!!
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
i think cos^2  1
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
\[2\cos^2 x1\]
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
so how will i substitute it to that equation?
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
cosA=2cos^2(A/2)1 find cos(A/2) from here.
 2 years ago

AravindG Group TitleBest ResponseYou've already chosen the best response.1
@sarihmanlapaz gt it?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
got it! thanks :)
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
but its none of the choices. >.< how can i solve it?
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
what did u get ?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
0.2435
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
i m getting 0.2435, is that the option ?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
oh no. haha my answer 0.2435 is in the options. i did'nt notice it.
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
but A/2 will be in 2nd quadrant where cos is negative. so we put minus 0.2435
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
its written in the question that the A is in quadrant 3
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
yes, A in 3rd,A/2 in 2nd. is 0.2435 in options?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
the options are. A).0.24054 B).0.24125 C) 0.24254 D) 0.24354
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
pls can you help me?
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
since all options are positive, i guess A/2 goes in 1st quadrant...then 0.2435 is correct.
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
no. its wrong my friend. i just check the half angle formula. haha there is a formula for cosA/2 = squareroot of 1/2(1+A)
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
u mean ....(1+cos A) ?
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
yes. yes :) i got the right answer 0.2425
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
how? the formula we gave and what u wrote are exactly the same...
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
http://www.themathpage.com/atrig/trigonometricidentities.htm
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
there is the formula for half angle :)
 2 years ago

hartnn Group TitleBest ResponseYou've already chosen the best response.0
so using that u got different answer? we gave u that formula only..... cosA=2cos^2(A/2)1 so cos(A/2)=sqrt{0.5*(1+cos A)}
 2 years ago

sarihmanlapaz Group TitleBest ResponseYou've already chosen the best response.0
yeah. thanks i got the right answer.
 2 years ago
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
 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.