Question

second and fourth term of an ap is 12 and 20 respectively find the sum of first 25 terms of that AP.​

Answer 1

1400 answers ,first term= 8 and d=4

Answer 2

Answer:

Sum of first $25$ terms of the given AP is $1400$

Step-by-step explanation:

Given second term $a+d=12$

and fourth term $a+3d=20$.

subtracting these two equations ,we get

$a+3d=20\ -\\a+d=12$

⇒ $2d=8$

hence $d=4$. And hence $a=12-4=8$.

Sum of first $25$ terms $=S_{25} =\frac{n}{2}[2a+(n-1)d]$

                                            $=\frac{25}{2} [2(8)+24(4)]\\\\=\frac{25}{2} [16+96]\\\\=25(56)\\\\=1400$

Hence the answer

thank you