Question

3n^2+6n find the sum of the first 15 terms in this case

Answer 1

Answer:

$3n ^{2} + 6n \\ 9n ^{2} + 6n{here \: first \: we \: have \: 2as \: the \: whole \: power \: but \: it \: is \: only \: n ^{2}$

Answer 2

Answer:

nth term=3n²+6n

so 1st term will be=t1=3(1²)+6*1=9

so the second term will be=t2=3(2²)+6*2=24

d=t2-t1

d=24-9=15

so sum of first 15 terms=n/2(2t1+(n-1)d)

s₁₅=15/2(2*9+(15-1)15)

s₁₅=15/2(18+210)

s₁₅=15/2(228)

s₁₅=15*114

s₁₅=1710

thus, the sum of first 15 terms of the given A.P is=1710

Read more on Brainly.in - https://brainly.in/question/11848700#readmore

Step-by-step explanation: