document.write( "Question 1031119: sen(a)= 8/17, 0 < a < π/2 and cos(B) = 3/5, 0 < B < π/2, cos (a+b)= ??? \n" ); document.write( "

Algebra.Com's Answer #645840 by ikleyn(52794) $\"\"$ $\"About$

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\n" ); document.write( "sin(a)= 8/17, 0 < a < pi/2 and cos(b) = 3/5, 0 < B < pi/2, cos (a+b)= ???
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document.write( "1.  We are going to use the formula \r\n" );
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document.write( "   cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b)\r\n" );
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document.write( "   (regarding this formula, see the lesson  Addition and subtraction formulas  in this site).\r\n" );
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document.write( "   For it, we need  cos(a)  and  sin(b),  in addition to the given  sin(a)  and  cos(b).\r\n" );
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document.write( "2.  cos(a) =  =  =  =  =  = .\r\n" );
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document.write( "    The sign \"+\" was chosen for the square root since the angle \"a\" is in Q1.\r\n" );
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document.write( "3.  sin(b) =  =  = .\r\n" );
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document.write( "    The sign \"+\" was chosen for the square root since the angle \"b\" is in Q1.\r\n" );
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document.write( "4.  Now  cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b) =  =  =  = .\r\n" );
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