Question

2
V
(A) 16 m
11. In an A.P., the first term is 1 and the common difference is 4. How many termint
A.P. must be taken for their sum to be equal to 120?
(A) 6
(B) 7
(0)8
(D) 9​

Answer 1

Answer:

C) 8

Step-by-step explanation:

a=1, d=4

Sn = 120

n(2a+(n-1)d)/2 = 120

n = 240/2+(n-1)4

n(2+4n-4) = 240

2n + 4n² - 4n = 240

4n² - 2n - 240 = 0

2n² - n - 120 = 0

2n² - 16n + 15n - 120 = 0

2n(n - 8) + 15(n - 8) = 0

(n-8)(2n+15) = 0

n = 8 or -15/2

n should be a natural number. so n = 8

so 8 terms should be taken to get sum equal to 120

I hope you have understood and will mark this answer as Brainliest answer