document.write( "Question 1016403: the 4th term of an A.P is 15 and the 9th term is 35. Find the fifteenth term? \n" ); document.write( "

Algebra.Com's Answer #633097 by ikleyn(52790) $\"\"$ $\"About$

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\n" ); document.write( "the 4th term of an A.P is 15 and the 9th term is 35. Find the fifteenth term?
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document.write( "Apply the formula  =  for the n-th term of an AP. You will have\r\n" );
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document.write( " =  +  = 15.   (1)\r\n" );
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document.write( " =  +  = 35.   (2)\r\n" );
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document.write( "Take the difference (2) - (1). You will have\r\n" );
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document.write( "8d - 3d = 35 - 15  --->  5d = 20  --->  d =  = 4.\r\n" );
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document.write( "Thus we just found the common difference.\r\n" );
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document.write( "Now,  =  =  +  =  +  = 35 + 6*4 = 35 + 24 = 59.\r\n" );
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document.write( "Answer.  = 59.\r\n" );
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