Question

How many terms of the sequence –57, –54, –51, ........ should be taken to get their sum equal to zero?

Answer 1

Answer:

-57, -54, -51, -48, -45, -4

Answer 2

Answer:

39

Step-by-step explanation:

a= 57

d= -3

Sn= 0

$sn = \frac{n}{2} (2a + (n - 1)d) \\ 0 = \frac{n}{2} (2 \times 57 + (n - 1)( - 3))$

0= n(114 -3 n +(-3))

0 = n (117 - 3n)

0 = 117n - 3n²

0 = 3n ( 39- n)

3n = 0 or 39- n =0

n = 0 or n = 39

n= 0 ( not possible)

so, n= 39