document.write( "Question 1172505: the 7th term of an ap is 17 and the13th term is 12 more than the 7th term find the 21st term of the ap \n" ); document.write( "

Algebra.Com's Answer #797559 by Boreal(15235) $\"\"$ $\"About$

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an=a1+(d(n-1), and 6 terms later the new value is 12 more, so d=2
\n" ); document.write( "so
\n" ); document.write( "a7=17=a1+2(6)
\n" ); document.write( "a1=5
\n" ); document.write( "Can also figure it that if the 13 th term is 12 more than the 7th, the 7th is 12 more than the first,
\n" ); document.write( "a21=5+2(20)=45.\r
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