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 December 10th, 2009, 12:10 PM #1 Newbie   Joined: Dec 2009 Posts: 2 Thanks: 0 How can solve this simple equation please step by step -A cos 30° + B cos 45° =0 A sin 30° + B sin 45° =147
December 10th, 2009, 01:15 PM   #2
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Re: How can solve this simple equation please step by step

Quote:
 Originally Posted by falcon -A cos 30° + B cos 45° =0 A sin 30° + B sin 45° =147
Plug in the specific values for the cos and sin of the given angles. (sin30° = 1/2 cos30° = ?(3)/2, sin 45°=cos45° = ?(2)/2) and solve linear equations. This is especially easy because sin45°=cos45°, so you have A(sin30° + cos30°) = 147. You should be able to finish.

 December 10th, 2009, 01:20 PM #3 Global Moderator   Joined: Dec 2006 Posts: 20,835 Thanks: 2162 Since cos 45° = sin 45°, subtracting the first equation from the second gives A(sin 30° + cos 30°) = 147. Hence A = 147/(sin 30° + cos 30°)              = 147(cos 30° - sin 30°)/(cos²30° - sin²30°)              = 147(cos 30° - sin 30°)/cos 60°              = 147((?3)/2 - 1/2)/(1/2)              = 147?3 - 147. From the first equation, B = A cos 30° / cos 45° = (147?3 - 147)((?3)/2)/(1/?2) = (441?2 - 147?6)/2.
 December 11th, 2009, 03:44 PM #4 Newbie   Joined: Dec 2009 Posts: 2 Thanks: 0 Re: How can solve this simple equation please step by step thanks for help

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