Question

135. The sum of n terms 1, 8, 27, 64, .......​

Answer 1

Answer:

a = 1

d = 8 - 1 = 7

$\tt{s_{n} = \frac{n}{2}(2a+(n-1)d)}$

=> $\tt{s_{n} = \frac{n}{2}(2+(n-1)7)}$

Answer 2

Step-by-step explanation:

Given, sum of n terms = 135

a1 = 1, a2 =8

then, common difference= a2 - a1

= 8 - 1 = 7

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

135 = n/2 [2*1 + (n - 1)7]

135*2 = n(2 + 7n - 7)

135*2 = n(7n - 5)

270 = 7n2 - 5n

7n2 - 5n - 270 = 0

factorise it and get your answer