Question

class 10 ap a=5 ,a13 =35,find d and s13

Answer 1

a13=35
a=5
"" "" "" "" "" "" "" "" "
an = a + (n-1)d
a13 = 5 + (13-1)d
35 = 5+ 12d
35-5=12d
30=12d
d=30/12
d= 5/2
""""""""""
Sn= n/2 (2a + (n-1)d )
S13 =13/2 ( 2×5 + (13-1)5/2 )
= 13/2 (10 + 12×5 /2 )
= 13/2 (10 + 30)
= 13/2 (40)
=520/2
=260
" "" "" "" "" "" "" "" "" "" "" ""
d = 5/2
S13= 260
""""""""""""""""""""""""""""""""

Answer 2

Answer:

d= 7/3 and s13 = 273

Step-by-step explanation:

Here,

a=7 , n=13 , a13= 35 , d=? and s13 = ?

As we know ,

a13 = a+(13-1)d (By substituting)

35 = 7+12d

-12d = 7-35

-12d = -28

d = 28/12

d = 7/3

ANS:7/3

since, Sum of n term of AP is:

Sn = n/2 [a+an]

Sn = 13/2 [7+a13]

= 13/2 [7+35]

=13/2 [ 42]

= 13×42/2

= 13×21

= 273

ANS: 273