Which term of AP 5,9,..........is81? And also find sum of 5+9+13+..........+81
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nth term = a+(n-1)d
5+(n-1)4 = 81,
5+4n-4=81
4n=80
n=80/4=20
so 81 is 20th term.
sum is n/2(a+l)
sum =20/2(5+81) = 10*86 =860.
5+(n-1)4 = 81,
5+4n-4=81
4n=80
n=80/4=20
so 81 is 20th term.
sum is n/2(a+l)
sum =20/2(5+81) = 10*86 =860.
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