Question

the sum of how many terms of the ap 7 11 15 19 23........will be 900​

Answer 1

Step-by-step explanation:

$\huge\underline{\underline{\sf ANSWER}} \\ a = 7 \\ t2 = 11 \\ d = t2 - a= 11- 7 = 4$

$Sn = \frac{n}{2} [2a + (n - 1)d] \\ 900 = \frac{n}{2} [14 + 4n - 4] \\ 1800 = 10 n + 4 {n}^{2} \\ 2 {n}^{2} + 5n - 1800 \\ n = \frac{126}{4} = \frac{23}{2} \: \: \: \: or \: \: \: \: n = \frac{116}{4} = 58 \\ \\ so \: n = 58 \\ \\ therefore \: sum \: of \: 58 \: terms \: is \: 900$