Asked by sandhya
find the sum to 20 terms of an A.P. whose 4th term is 7 and 7th term is 13
Answers
Answered by
Reiny
"4th term is 7" ---> a+3d = 7
"7th term is 13" ---> a+6d = 13
subtract them:
3d = 6
d = 2
sub back into my first equation to find a,
then use the Sum of Terms formula to find sum(20)
"7th term is 13" ---> a+6d = 13
subtract them:
3d = 6
d = 2
sub back into my first equation to find a,
then use the Sum of Terms formula to find sum(20)
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