document.write( "Question 1199202: This is a calculus question. Could you explain #16 on https://www.math.purdue.edu/php-scripts/courses/oldexams/serve_file.php?file=16200FE-F2021.pdf which is about finding the limit using series? \n" ); document.write( "
Algebra.Com's Answer #832950 by ikleyn(52803)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "(1)  Write several starting terms of the first series\r\n" );
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document.write( "         cos(x) = 1 - \"x%5E2%2F2\" + \"x%5E4%2F24\" - \"x%5E6%2F720\" .\r\n" );
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document.write( "     Replace here x with \"x%5E3\", since you want  \"cos%28x%5E3%29\".  You will get\r\n" );
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document.write( "         \"cos%28x%5E3%29\" = 1 - \"x%5E6%2F2\" + \"x%5E12%2F24\" - \"x%5E18%2F720\".           (1)\r\n" );
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document.write( "     You should keep as many terms of this series to have at least the term with \"x%5E12\".\r\n" );
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document.write( "(2)  Write several starting terms of the second series\r\n" );
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document.write( "         \"tan%5E%28-1%29%28x%29\" = \"x\" - \"x%5E3%2F3\" + \"x%5E5%2F5\" .\r\n" );
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document.write( "     Replace here x with \"x%5E6%2F2\", since you want  \"tan%5E%28-1%29%28x%5E6%2F2%29\".  You will get\r\n" );
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document.write( "         \"tan%5E%28-1%29%28x%5E6%2F2%29\" = \"x%5E6%2F2\" - \"x%5E18%2F24\" + \"x%5E30%2F160\".          (2)\r\n" );
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document.write( "     You should keep as many terms of this series to have at least the term with \"x%5E12\".\r\n" );
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document.write( "(3)  Using (1) and (2), form   \"cos%28x%5E3%29\" + \"tan%5E%28-1%29%28x%5E6%2F2%29\" - \"1\".   You will get\r\n" );
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document.write( "         \"cos%28x%5E3%29\" + \"tan%5E%28-1%29%28x%5E6%2F2%29\" - \"1\" =  1 - \"x%5E6%2F2\" + \"x%5E12%2F24\" - \"x%5E18%2F720\" \r\n" );
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document.write( "                                             +  \"x%5E6%2F2\" - \"x%5E18%2F24\" + \"x%5E30%2F160\" - 1 =\r\n" );
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document.write( "         = some terms will cancel; other will remain; I will keep the remaining terms with \"x%5E12\".  It gives \r\n" );
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document.write( "         = \"x%5E12%2F24\".   The other terms have x in degrees HIGHER than 12.\r\n" );
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document.write( "(4)  After dividing by \"x%5E12\",  I have \"1%2F24\" plus other terms with x of degree higher than 1.\r\n" );
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document.write( "     When calculating the limit at x--> 0, these terms produce 0 (zero), so they are not interesting to me.\r\n" );
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document.write( "(5)  Thus I get the ANSWER:  the sough limit at  x --> 0  equals  \"1%2F24\".\r\n" );
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