Hey there! Sign in to join this conversationNew here? Join for free

inverse trig question Watch

Announcements
    • Thread Starter
    Offline

    12
    ReputationRep:
    here is question
    • Thread Starter
    Offline

    12
    ReputationRep:
    Name:  ds.PNG
Views: 16
Size:  2.0 KB
    where that 2 goes

    i know first to take inverse of sin sqroot 2/2
    then what to do of 2 with that?
    Online

    21
    ReputationRep:
    (Original post by Qer)
    Name:  ds.PNG
Views: 16
Size:  2.0 KB
    where that 2 goes

    i know first to take inverse of sin sqroot 2/2
    then what to do of 2 with that?
    sin(2x) = 2 cos x sin x
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    sin(2x) = 2 cos x sin x
    can you please show me working?. it will be easier for me to understand
    Online

    21
    ReputationRep:
    (Original post by Qer)
    can you please show me working?. it will be easier for me to understand
    No. Tell me what you've done so far. What is arcsin(sqrt(2)/2)? What is 2 times that? What is sin of that?
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    No. Tell me what you've done so far. What is arcsin(sqrt(2)/2)? What is 2 times that? What is sin of that?

    is it like that
    2 arcsin sqroot 2/2= 2 X 1/4pi = 1/2 pi
    sin( 1/2 pi)=1


    not sure that it is right?
    Online

    21
    ReputationRep:
    (Original post by Qer)
    is it like that
    2 arcsin sqroot 2/2= 2 X 1/4pi = 1/2 pi
    sin( 1/2 pi)=1


    not sure that it is right?
    It is. See, all you had to do was try it yourself.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    It is. See, all you had to do was try it yourself.

    can i ask some more questions?
    Online

    21
    ReputationRep:
    (Original post by Qer)

    can i ask some more questions?
    Sure. As long as you lay out your current working/thoughts for them.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    Sure. As long as you lay out your current working/thoughts for them.
    Name:  m.PNG
Views: 13
Size:  17.7 KB

    so
    i am ok with part a . as we can see from graph

    for part b
    i
    cos^2k =1- sin^2k
    taking sqroot
    cos k= 1- sin k

    the book shows answer is +- sqroot(1-sin^2 k)

    why they dont cancel sqroot?

    part c doesnt make any sense to me
    Online

    21
    ReputationRep:
    (Original post by Qer)
    Name:  m.PNG
Views: 13
Size:  17.7 KB

    so
    i am ok with part a . as we can see from graph

    for part b
    i
    cos^2k =1- sin^2k
    taking sqroot
    cos k= 1- sin k

    the book shows answer is +- sqroot(1-sin^2 k)

    why they dont cancel sqroot?

    part c doesnt make any sense to me
    sqrt(1-sin^2 k) is not the same thing as 1 - sin k.

    Do you think that sqrt(1-0.5^2) = 1 - 0.5?
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    sqrt(1-sin^2 k) is not the same thing as 1 - sin k.

    Do you think that sqrt(1-0.5^2) = 1 - 0.5?
    ok
    that make sense now
    Online

    21
    ReputationRep:
    (Original post by Qer)
    ok
    that make sense now
    You know that if 0<k<pi/2 then cos k is a positive number, which is why cos k = sqrt(1- sin^2 k)

    If -pi/2 < k < 0, what is the sign of cos k? Check a graph. Is it under/below the k-axis in that interval?
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    You know that if 0<k<pi/2 then cos k is a positive number, which is why cos k = sqrt(1- sin^2 k)

    If -pi/2 < k < 0, what is the sign of cos k? Check a graph. Is it under/below the k-axis in that interval?
    how i make graph of function cos k = sqrt(1- sin^2 k)?
    Online

    21
    ReputationRep:
    (Original post by Qer)
    how i make graph of function cos k = sqrt(1- sin^2 k)?
    No, make a graph of the function cos k.
    • Thread Starter
    Offline

    12
    ReputationRep:
    dran
    (Original post by Zacken)
    You know that if 0<k<pi/2 then cos k is a positive number, which is why cos k = sqrt(1- sin^2 k)

    If -pi/2 < k < 0, what is the sign of cos k? Check a graph. Is it under/below the k-axis in that interval?
    graph is in second quadrant ( above the axes) so it is positive
    Online

    21
    ReputationRep:
    (Original post by Qer)
    drangraph is in second quadrant ( above the axes) so it is positive
    Right, so there's no difference to your answer. cos k = sqrt(1 - sin^2 k)

    You just need to rewrite sin^2 k in terms of x.
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    Right, so there's no difference to your answer. cos k = sqrt(1 - sin^2 k)

    You just need to rewrite sin^2 k in terms of x.
    there is also tan in par b
    is this answer for both of them?
    Online

    21
    ReputationRep:
    (Original post by Qer)
    there is also tan in par b
    is this answer for both of them?
    You tell me. Is tan k positive for 0<k<pi/2? What about for -pi/2 < k < 0?
    • Thread Starter
    Offline

    12
    ReputationRep:
    (Original post by Zacken)
    You tell me. Is tan k positive for 0<k<pi/2? What about for -pi/2 < k < 0?
    Is tan k positive for 0<k<pi/2?
    it is positive

    -pi/2 < k < 0?
    in that range it is below the axes so it is negative?
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Should Spain allow Catalonia to declare independence?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.