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November 26th, 2008, 03:58 PM  #1 
Newbie Joined: Nov 2008 Posts: 4 Thanks: 0  Quick high school math question... ? and ? are acute angles in quadrant I, with sin ? = 7/25 and cos B = 5/13. Determine the value of sin (? + ?) The answer is 323 / 325 I started with sin (? + ?) = sin ? cos ? + cos ? sin ? ? = 7/25 B = 5/13 sin (7/25) cos (5/13) + cos (7/25) sin (5/13) ...but, where do you go from there? 
November 26th, 2008, 05:22 PM  #2  
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,968 Thanks: 1152 Math Focus: Elementary mathematics and beyond  Re: Quick high school math question... Quote:
B = cos^1(5/13) sin(a + B) = 323/325  
November 27th, 2008, 05:47 PM  #3  
Senior Member Joined: Jul 2008 Posts: 895 Thanks: 0  Re: Quick high school math question... Quote:
You have sin (? + ?) = sin ? cos ? + cos ? sin ? You know sin a, so you need from that cos a. You know cos B, so you need from that sin B. Draw right triangle for each case separately, one containing angle a, and one containing angle B, and label sides from the given ratios. Find the third side using Pythagoras, and then find the missing trig functions. Dave.  

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