Question

If the sum of the first n terms of an arithmetic progression is given by the equation
15n + 3n2, then what is the 18th element of this AP?​

Answer 1

Step-by-step explanation:

whether question is correct...........

Answer 2

Answer:

3n2+2n

Taking n=1, we get 

S1=3(1)2+2(1)

⇒S1=3+2

⇒S1=5

⇒a1=5

Taking n=2, we get 

S2=3(2)2+2(2)

⇒S2=12+4

⇒S2=16

∴a2=S2−S1=16−5=11

Taking n=3, we get 

S3=3(3)2+2(3)

⇒S3=27+6

⇒S3=33

∴a3=S3−S2=33−16=17

So, a=5,

d=

Step-by-step explanation:

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