Question

The sum of 2nd and 19th term of an arithmetic sequence is 82.
(a) What is the sum of 1st and 20th terms ?
(b) Find the sum of first 20 terms of the sequence.
(c) If the 10th term is 39. What is the 11th term ?
(d) Find the first term.​

Answer 1

Answer:

Given,

a

1

+a

20

=88

a.

a

2

+a

19

=(a

1

+d)+(a

20

−d)

=a

1

+a

20

=88

b.

a

10

+a

11

=a

1

+9d+a

20

−9d

42+a

11

=a

1

+a

20

∴a

11

=88−42=46

c.

d=a

11

−a

10

=46−42=4

d.

a

10

=a+9d

a=42−9(4)

∴a=6

Answer 2

Answer:

[tex]a. \\ \\ a_{2} + a_{19} \\ =(a1+d)+(a20−d) \\ =a _{1}+a_{20} = 88