Math, asked by mageshsuresh2020, 1 month ago

In an A.P the first term is I and the common difference is 4. How many terms of the A.P must be taken for their sum to be equal to 120? (1) 6 (2) 7 (3) 8 (4) 9​

Answers

Answered by JigyashaJain
0

Answer:

3) n = 8

Step-by-step explanation:

a = 1

d = 4

Sn = 120

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

120 = n/2 [2×1 + (n-1)4]

120 = n/2 [2 + 4n - 4]

120 = n/2 [4n - 2]

120×2 = n(4n - 2)

240 = 4n² - 2n

4n² - 2n - 240 = 0

2(2n² - n - 120) = 0

2n² - n - 120 = 0

2n² - 16n + 15n - 120 = 0

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

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

n = -15/2 , 8

n can't be in fraction. Therefore, n is 8.

Answered by hariuthiras
2

Answer:

8

Step-by-step explanation:

The value of n is 8. So, 8 terms of the A.P must be taken for their sum to be equal to 120.

Similar questions