SOLUTION: 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

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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
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
an=a1+(d(n-1), and 6 terms later the new value is 12 more, so d=2
so
a7=17=a1+2(6)
a1=5
Can also figure it that if the 13 th term is 12 more than the 7th, the 7th is 12 more than the first,
a21=5+2(20)=45.