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 November 10th, 2011, 07:56 AM #1 Member   Joined: Nov 2011 Posts: 37 Thanks: 0 Help with Trignometric Ratios Determine the exact value of each Trig ratio: 1) Sin 2?/3 2) Cos 7?/6 3) Sin 5?/4 4) Tan 4?/3 5) Sec 7?/6 November 10th, 2011, 09:39 AM #2 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,963 Thanks: 1148 Math Focus: Elementary mathematics and beyond Re: Help with Trignometric Ratios Given cos(?/3) = 1/2, sin(?/3) = ?(3)/2, cos(?/4) = ?(2)/2, sin(?/4) = ?(2)/2, cos(?/6) = ?(3)/2 and sin(?/6) = 1/2 (from 'special' triangles) you may use the angle sum difference formulas for sin, cos and tan: sin(a � b) = sin(a)cos(b) � sin(b)cos(a). cos(a � b) = cos(a)cos(b) ? sin(a)sin(b). tan(a � b) = (tan(a) � tan(b))/(1 ? tan(a)tan(b)). Note: sin(?) = 0, cos(?) = -1. November 10th, 2011, 10:22 AM #3 Member   Joined: Nov 2011 Posts: 37 Thanks: 0 Re: Help with Trignometric Ratios Can you show me what you mean by solving one of these? November 10th, 2011, 10:28 AM #4 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,963 Thanks: 1148 Math Focus: Elementary mathematics and beyond Re: Help with Trignometric Ratios 2) cos(7?/6) = cos(?)cos(?/6) - sin(?)sin(?/6) = -?(3)/2. The other problems follow a similar pattern. November 10th, 2011, 10:49 AM #5 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,963 Thanks: 1148 Math Focus: Elementary mathematics and beyond Re: Help with Trignometric Ratios Another way of looking at it, you've got the angles shifted by ? so, for example, cos(7?/6) = cos(? + ?/6) = -cos(?/6) = -?(3)/2. November 10th, 2011, 12:17 PM   #6
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Re: Help with Trignometric Ratios

I recommend studying this too:

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Attached Images 600px-Unit_circle_angles_color.svg.png (91.1 KB, 119 views) Tags ratios, trignometric Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post ashu Calculus 15 September 24th, 2012 12:24 AM layd33foxx Calculus 1 February 21st, 2012 05:33 PM prashantakerkar Trigonometry 5 November 15th, 2011 12:20 AM becko Complex Analysis 3 August 19th, 2010 01:13 PM n30 Algebra 4 December 22nd, 2007 04:12 PM

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