document.write( "Question 873142: find the exact value of cos(a+B)
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Algebra.Com's Answer #526656 by Edwin McCravy(20056)\"\" \"About 
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document.write( "find the exact value of cos(a+B)\r\n" );
document.write( "if sin a= -4/5, and sin B= 5/13\r\n" );
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document.write( "cos(a) = ±√1-sinČ(a) = \"%22%22+%2B-+sqrt%281-%28-4%2F5%29%5E2%29\" = \"%22%22+%2B-+sqrt%281-16%2F25%29%29\" = \"%22%22+%2B-+sqrt%2825%2F25-16%2F25%29%29\" = \"%22%22+%2B-+sqrt%289%2F25%29%29\" = \"%22%22+%2B-+3%2F5%29\"\r\n" );
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document.write( "cos(B) = ±√1-sinČ(B) = \"%22%22+%2B-+sqrt%281-%285%2F13%29%5E2%29\" = \"%22%22+%2B-+sqrt%281-25%2F169%29%29\" = \"%22%22+%2B-+sqrt%28169%2F169-25%2F169%29%29\" = \"%22%22+%2B-+sqrt%28144%2F169%29%29\" = \"%22%22+%2B-+12%2F13%29\" \r\n" );
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document.write( "Case 1:  a is in Q3 and B is in Q1\r\n" );
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document.write( "cos(a+B) = cos(a)cos(B) - sin(a)sin(B) = (-3/5)(12/13) - (-4/5)(5/13) = -16/65\r\n" );
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document.write( "Case 2:  a is in Q3 and B is in Q2\r\n" );
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document.write( "cos(a+B) = cos(a)cos(B) - sin(a)sin(B) = (-3/5)(-12/13) - (-4/5)(5/13) = 56/65\r\n" );
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document.write( "Case 3:  a is in Q4 and B is in Q1\r\n" );
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document.write( "cos(a+B) = cos(a)cos(B) - sin(a)sin(B) = (3/5)(12/13) - (-4/5)(5/13) = 56/65\r\n" );
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document.write( "Case 4:  a is in Q4 and B is in Q2 \r\n" );
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document.write( "cos(a+B) = cos(a)cos(B) - sin(a)sin(B) = (3/5)(-12/13) - (-4/5)(5/13) = -16/65\r\n" );
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document.write( "Two possible solutions: -16/65 and 56/65\r\n" );
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document.write( "Edwin
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