document.write( "Question 1142527: Prove that the surface area of a cone without its base circle is A=pirs, where r is the base radius and s is the slant height of the cone.\r
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Algebra.Com's Answer #763216 by ikleyn(52781)\"\" \"About 
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document.write( "The basic formula for the lateral surface area of a cone is\r\n" );
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document.write( "    A = \"%281%2F2%29%2AH%2As\",      (1)\r\n" );
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document.write( "where A is the lateral surface area, H is the slant height and \"s\" is the circumference of the base of the cone.\r\n" );
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document.write( "When students study the lateral surface area of a cone, they start from this formula, so I will assume that you are familiar with it.\r\n" );
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document.write( "    If not, then you can derive it mentally and momentarily in your mind, presenting the lateral surface area \r\n" );
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document.write( "    of  cone as the union of surface area of many narrow triangles with the common peak vertex at the cone's vertex.\r\n" );
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document.write( "The last step in my explanation is the formula  \r\n" );
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document.write( "    s = \"2%2Api%2Ar\"      (2)\r\n" );
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document.write( "for the base circumference.  Here  \"r\"  is the cone's radius (= the radius of the base).\r\n" );
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document.write( "As soon as you substitute  (2)  into (1), you will obtain what you need.\r\n" );
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