Question

A=7,a13=35,find d and s13 step by step

Answer 1

i) given a=7, a13=35
a13 (or)  a+12d = 35 ------- 1
a = 7 (or) a+0d = 7  ------- 2
by subtracting 1 with 2 we get
           
                   a+12d = 35
                   a+  0d = 07
                 -       -      -
                  ------------------
                        12d = 28
                  -------------------
 d = 28/12 = 2.33
so,  d = 2 (approximately)

S13 = n/2 [a+l]
n=13, a= 7, a13 = l = 35
S13 = 13/2 [7+35]
S13 = 13/2 [42]
S13 = 13 [21]
therefore, S13 = 273

Hope it helps. Plz mark me as brainliest.

Answer 2

Answer:

d = 7/3, Sn=273

Step-by-step explanation:

First term of an AP = a = 7

Thirteenth term of an AP = 35

a + 12d = 35 ------(1)

Substitute a in eq - (1)

a + 12d = 35

(7) + 12d = 35

12d = 35 - 7

12d = 28

d = 28/12

d = 7/3

In an AP sum of the terms = n/2 ( a + an )

= 13/2 ( 7 + 35)

= 13/2 ( 42)

= 13(21)

= 273