Question

if Sn= 3n2+5n.find its 25th term

Answer 1

Answer:

25th term = 152

Step-by-step explanation:

Sn = 3n² + 5n

n = 1

S1 = 3(1²) + 5(1) = 3 + 5 = 8

n = 2

S2 = 3(2²) + 5(2) = 12 + 10 = 22

n = 3

S3 = 3(3²) + 5(3) = 27 + 15 = 42

S1 = 8 = a1

S2 = 22 = a2 = a + a + d = 8 + 8 + d = 16 + d

16 + d = 22

d = 22 - 16

d = 6

25th term = a + 24d

= 8 + 24(6)

= 8 + 144

= 152

therefore the 25th term is 152

Hope you get your answer