document.write( "Question 1036430: Evaluate the expression under the given conditions\r
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Algebra.Com's Answer #651112 by ikleyn(52797)\"\" \"About 
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document.write( "To evaluate  \"sin%28theta-phi%29\"  you will use the formula \r\n" );
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document.write( "\"sin%28theta-phi%29\" = \"sin%28theta%29%2Acos%28phi%29+-+cos%28theta%29%2Asin%28phi%29\".     (1)\r\n" );
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document.write( "To use this formula, you need to know  \"sin%28theta%29\",  \"cos%28phi%29\",  \"cos%28theta%29\"  and  \"sin%28phi%29\".\r\n" );
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document.write( "Is it given to you? - Only in part: you are given  \"\"sin%28phi%29\" = \"-sqrt%2810%29%2F10\"  and  \"phi\" is in Q4\".\r\n" );
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document.write( "Regarding  \"theta\", you are given that  \"\"tan%28theta%29\" = \"12%2F5\"  and  \"theta\" is in Q3\".\r\n" );
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document.write( "So, your first task is, based on the given data, find  \"sin%28theta%29\",  \"cos%28theta%29\"  and  \"cos%28phi%29\".\r\n" );
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document.write( "You have  \"sin%28theta%29\" = \"-sqrt%281%2F%281+%2B+1%2Ftan%5E2%28theta%29%29%29\" = \"-sqrt%28+1%2F%281+%2B+%285%2F12%29%5E2%29%29\" = \"-sqrt%281%2F%28%281%2B+25%2F144%29%29%29\" = \"-sqrt%28144%2F169%29\" = \"-12%2F13\".\r\n" );
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document.write( "   The sign \"-\" was chosen for the square root, because the sine  is negative for an angle in Q3.\r\n" );
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document.write( "Having \"sin%28theta%29\" = \"-12%2F13\", you can easily calculate \r\n" );
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document.write( "\"cos%28theta%29\" = \"-sqrt%281+-+sin%5E2%28theta%29%29\" = \"-sqrt%281+-+%28-12%2F13%29%5E2%29\" = \"-sqrt%281+-+144%2F169%29\" = \"-sqrt%28%28169-144%29%2F169%29\" = \"-sqrt%2825%2F169%29\" = \"-5%2F13\".\r\n" );
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document.write( "   The sign \"-\" was chosen for the square root, because the cosine  is negative for an angle in Q3.\r\n" );
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document.write( "Next,  \"cos%28phi%29\" = \"sqrt%281+-+sin%5E2%28phi%29%29\" = \"sqrt%281+-+%28-sqrt%2810%29%2F10%29%5E2%29\" = \"sqrt%281+-+%2810%2F100%29%29\" = \"sqrt%2890%2F100%29\" = \"%283%2Asqrt%2810%29%29%2F10\".\r\n" );
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document.write( "   The sign \"+\" was chosen for the square root, because the cosine is positive for an angle in Q4.\r\n" );
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document.write( "Let us summarize what we have so far:  \"sin%28theta%29\" = \"-12%2F13\",   \"cos%28phi%29\" = \"%283%2Asqrt%2810%29%29%2F10\",  \"cos%28theta%29\" = \"-5%2F13\"  and   \"sin%28phi%29\"= \"-sqrt%2810%29%2F10\".\r\n" );
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document.write( "Now you can plug-in this data into the formula (1) and get\r\n" );
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document.write( "\"sin%28theta-phi%29\" =  = \"-%2812%2A3%2Asqrt%2810%29%29%2F130+-+%285%2Asqrt%2810%29%29%2F130\" = \"-%28%2836%2B5%29%2Asqrt%2810%29%29%2F130\" = \"-%2841%2Asqrt%2810%29%29%2F130\". \r\n" );
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document.write( "Answer.  \"sin%28theta-phi%29\" = \"-%2841%2Asqrt%2810%29%29%2F130\".\r\n" );
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\n" ); document.write( "\n" ); document.write( "For many other similar problems see 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
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