SOLUTION: the 6th term of an ap is 29 and 13th term is 64. calculate the first term common difference and the sum of the first 20 terms

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Question 1053537: the 6th term of an ap is 29 and 13th term is 64. calculate the first term common difference and the sum of the first 20 terms
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a%5B6%5D=a%5B1%5D%2B%286-1%29%2Ad=29
a%5B1%5D%2B5d=29
.
.
a%5B13%5D=a%5B1%5D%2B%2813-1%29%2Ad=64
a%5B1%5D%2B12d=64
Subtracting the previous equation from this one,
a%5B1%5D%2B12d-a%5B1%5D-5d=64-29
7d=35
d=5
Then,
a%5B1%5D%2B5%285%29=29
a%5B1%5D%2B25=29
a%5B1%5D=4
So then,