Question

nth term of an AP is an = (3n + 7).

i) The first term fo the given AP is

a) 10 b) -9 c) 12 d) -10.

ii) The common difference of the given AP is

a) 4 b) -4 c) -3 d) 3.

iii) The difference between a11 from a16 is

a) 18 b) 10 c) 15 d) 20

iv) Sum of 1st eight terms is

a) 140 b) 164 c) 400 d) 146.

v) Which term of the given AP is 40.

a) 13th term b) 10th term c) 11th term d) 20th term​

Answer 1

Answer:

iam not sure

Step-by-step explanation:

1.10

2.-3

3. 15

4. 400

5. 20

Answer 2

Answer:

i) a

ii) d

iii) c

iv) b

v) c

Step-by-step explanation:

i) put n = 1

a1 = 3(1) + 7 = 10

ii) a2 = 3(2) + 7 = 13

d = a2 - a1 = 13-10 = 3

iii) a16 - a11 = 3(16) - 3(11) since +7-7 will be cancelled

= 3(16-11) = 3(5) = 15

iv) S8 = n/2[ 2a + (n-1)d]

= 4[2(10) + (8-1) × 3]

= 4(20 + 21) = 164

v) at = a + (n-1) × d

40 = 10 + (n-1) x 3

30 = 3n - 3

3n = 33

n = 11