document.write( "Question 1171626: cos(a) =-4/5 and a is in quadrant II and sin(b)=5/13 and b is in quadrant II. Find cos(a+b)
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Algebra.Com's Answer #796578 by ikleyn(52832)\"\" \"About 
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document.write( "For angle  \" a \"  in QII, \r\n" );
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document.write( "    sin(a) = \"sqrt%281-cos%5E2%28a%29%29\" = \"sqrt%281-%28-4%2F5%29%5E2%29\" = \"sqrt%281-16%2F25%29\" = \"sqrt%289%2F25%29\" = \"3%2F5\"  (positive value).\r\n" );
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document.write( "For angle  \" b \"  in QII, \r\n" );
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document.write( "    cos(b) = - \"sqrt%281-sin%5E2%28b%29%29\" = - \"sqrt%281-%285%2F13%29%5E2%29\" = - \"sqrt%281-25%2F169%29\" = - \"sqrt%28144%2F169%29\" = - \"12%2F13\"  (negative value).\r\n" );
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document.write( "Now use  cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b).\r\n" );
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document.write( "Substitute the values into the formula and calculate.\r\n" );
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\n" ); document.write( "\n" ); document.write( "To see many other similar solved problems on calculating trig functions,  look into the lessons \r
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\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook in ALGEBRA-II in this site\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this online textbook under the topic  \"Trigonometry: Solved problems\". \r
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