the 35th term of an ap is 69. find the sum of its 69 terms
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The formula to calculate nth term in AP is tn=a+(n-1)d
where a is the first term
d is the common difference between two terms
d=tn-t(n-1)
and
Sn = (n/2)[2a+(n-1)d]
__________________________________________
Given,
t35=69
a+(35-1)d=69
a+34d=69==> eq 1
Also given,
S69=(69/2)[2a+(69-1)d]
=(69/2)[2a+68d]
=(69/2)*2(a+34d)
=69(a+34d) [ from eq 1 ]
= 69*69
=4761
So, Finally summer of 69 terms is 4761
Hope you understood it
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where a is the first term
d is the common difference between two terms
d=tn-t(n-1)
and
Sn = (n/2)[2a+(n-1)d]
__________________________________________
Given,
t35=69
a+(35-1)d=69
a+34d=69==> eq 1
Also given,
S69=(69/2)[2a+(69-1)d]
=(69/2)[2a+68d]
=(69/2)*2(a+34d)
=69(a+34d) [ from eq 1 ]
= 69*69
=4761
So, Finally summer of 69 terms is 4761
Hope you understood it
# Mark Me!!
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