document.write( "Question 1094865: could you please help me with this question\r
\n" ); document.write( "\n" ); document.write( "If x is in Quadrant IV with cos(x) = 3/5 and y is in Quadrant III with sin(y) = −2/√5, find cos(x+y)\r
\n" ); document.write( "\n" ); document.write( "I keep on getting -2√5 but that answer is not correct \n" ); document.write( "
Algebra.Com's Answer #709452 by ikleyn(52835)\"\" \"About 
You can put this solution on YOUR website!
.
\n" ); document.write( "
\r\n" );
document.write( "1.  \"x is in Quadrant IV with cos(x) = 3/5\"  ====>  sin(x) = \"sqrt%281-cos%5E2%28x%29%29\" = \"sqrt%281-%283%2F5%29%5E2%29\" = \"-4%2F5\".\r\n" );
document.write( "\r\n" );
document.write( "    The sign is \"-\" since sine is negative in QIV.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "2.  \"y is in Quadrant III with sin(y) = \"-2%2Fsqrt%285%29\"\"  ====>  cos(y) = \"sqrt%281-sin%5E2%28y%29%29\" = \"sqrt%281-4%2F5%29\" = \"-1%2Fsqrt%285%29\".\r\n" );
document.write( "\r\n" );
document.write( "    The sign is \"+\" since cosine is negative in QIII.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "3.  cos(x+y) = cos(x)*cos(y) - sin(x)*sin(y) = \"%283%2F5%29%2A%28-1%2Fsqrt%285%29%29+-+%28-4%2F5%29%2A%28-2%2Fsqrt%285%29%29\" = \"-3%2F%285%2Asqrt%285%29%29+-+8%2F%285%2Asqrt%285%29%29\" = \"-11%2F%285%2Asqrt%285%29%29\" = \"-11sqrt%285%29%2F25\".\r\n" );
document.write( "
\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "To see more solved similar problems on calculating trig functions, look into the lessons \r
\n" ); document.write( "\n" ); document.write( "    - Calculating trigonometric functions of angles\r
\n" ); document.write( "\n" ); document.write( "    - Advanced problems on calculating trigonometric functions of angles\r
\n" ); document.write( "\n" ); document.write( "    - Evaluating trigonometric expressions \r
\n" ); document.write( "\n" ); document.write( "in this site.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook in ALGEBRA-II in this site\r
\n" ); document.write( "\n" ); document.write( "    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this online textbook under the topic  \"Trigonometry: Solved problems\". \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Save the link to this textbook together with its description\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Free of charge online textbook in ALGEBRA-II
\n" ); document.write( "https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "into your archive and use when it is needed.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );