Question

Find the sum of the first
(i) 11 terms of the A.P : 2,6,10,14,...
(ii) 13 terms of the A.P : -6,0,6,12,...
(iii) 51 terms of the A.P. whose second term is 2 and fourth term is 8.

Answer 1

(i)=42

(ii)=66

(iii)=149

Step-by-step explanation:

(i) In the given A.P 2,6,10,14..........

To find $11^{th}$ term =?

given that a=2 d=4 {$\therefore$$a_{2}-a_{1}$}

for $11^{th}$ term=$a+10d$

$2+10\times 4$

$2+40$

$42$

(ii) $a=-6,d=6$

for $13th$ term

$a+12d$

$-6+12\times 6$

$-6+72$

$66$

(iii) Whose $2_{nd}$ term is $2$

$4^{th}$ term is $8$

for $5^{th}$ term=$a+50d$

according to question equation is given below

 $a+d=2-(i)\\a+3d=8-(ii)$

after solving equation (i) and (ii)

we get,$d=3$

put $d=3$ in equation (i)

$a+d=2\\a+3=2\\ a=-1$

  $a+50d$

$-1+50\times 3$

$-1+150$          

     $149$          

Answer 2

first s11=242

second s13=390

third s51=3774Answer:

Step-by-step explanation:plz mark meas brainlist