Question

In an Ap a=7,a13=35find d and s13?

Answer 1

a13 = a + 12d

35 = 7 + 12d

12d = 28 eq - i

d = 28/12 = 7/3

S13 = 13/2{2a + (13-1)d}

S13 = 13/2{14 + 12d}

now put value of 12d from eq i

S13 = 13/2(14 + 28)

S13 = (13/2)(42)

S13 = 273

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