in an Ap the sum of first n terms is 3n2/2+13n/2.find the 25th term
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mark brainiest
mark brainiest
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sn = 3n²/2 +13n/2
s1 = 3*1²/2+13*1/2 =3/2+13/2 = 16/2 = 8
s2 = 3*2²/2 + 13*2/2 = 6+13 =19
s3 = 3*3²/2 + 13*3/2 =27/2 +39/2 =66/2 =33
first term = a1 = s1 = 8
a2 = s2-s1 = 19-8 = 11
a3 = s3- s2 = 33 -19 =14
8,11,14,...are in Ap
first term = a = 8
common difference = d= a2-a1 = 11-8 =3
nth term = an = a +(n-1) d
25 th term = a25 = 8+(25-1) 3
= 8+24*3
= 8+72
=80
25 th term is =80
s1 = 3*1²/2+13*1/2 =3/2+13/2 = 16/2 = 8
s2 = 3*2²/2 + 13*2/2 = 6+13 =19
s3 = 3*3²/2 + 13*3/2 =27/2 +39/2 =66/2 =33
first term = a1 = s1 = 8
a2 = s2-s1 = 19-8 = 11
a3 = s3- s2 = 33 -19 =14
8,11,14,...are in Ap
first term = a = 8
common difference = d= a2-a1 = 11-8 =3
nth term = an = a +(n-1) d
25 th term = a25 = 8+(25-1) 3
= 8+24*3
= 8+72
=80
25 th term is =80
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