October 6th, 2010, 09:45 PM  #1 
Member Joined: Sep 2010 Posts: 55 Thanks: 0  stuck on a problem
Suppose u is an angle in the second quadrant and sin u=3/4. So cos u=? I'm lost on this one. How do I find cos u? I know that it is negative, but I don't know how to find the answer. 
October 6th, 2010, 09:48 PM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: stuck on a problem
The equation sin²u + cos²u = 1 is true for all u.

October 6th, 2010, 10:16 PM  #3 
Member Joined: Sep 2010 Posts: 55 Thanks: 0  Re: stuck on a problem
So sin^2 is 9/16. cos^2=7/16. So cos u=sqrt(7)/4. I keep putting that in but it isn't right. What am I doing wrong?

October 6th, 2010, 10:19 PM  #4 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,204 Thanks: 511 Math Focus: Calculus/ODEs  Re: stuck on a problem
Remember to use the negative root of cos²(u) = 7/16 since u is in quadrant II.


Tags 
problem, stuck 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Stuck on this problem.  sivela  Calculus  1  February 19th, 2012 10:21 PM 
Algebra problem. I'm stuck!  kreshnikk1  Algebra  3  January 18th, 2012 10:34 AM 
Stuck on a problem  INEEDHELP1  Calculus  1  September 30th, 2010 07:03 PM 
stuck on problem  adriana.alrb  Algebra  5  August 30th, 2009 10:14 PM 
Stuck on an Integration problem  Gotovina7  Calculus  5  February 17th, 2008 07:30 AM 