Question

how many terms of the series -9,-6,-3......must be taken so that the sum of them is 66

Answer 1

Answer:

20

Step-by-step explanation:

take all negative term

add them

-9 +( -6)+(-3)+0= -18

Now substract it with given number

66 - 18 = 48

Now

a = 3

Tn = 48

d = 3

Tn = a + (n - 1) d

48 = 3+ (n - 1)3

3(n - 1) = 45

n - 1= 15

n = 16

total term required = 16 + 4= 10

Answer 2

Answer:

a = 3

d = 3

-9 + -6 + -3 = -18

Tn = 66 - 18

= 48

Tn = a - (n - 1 ) d

48 = 3 - (n-1) 3

48 - 3 = ( n-1 ) 3

45 = 3( n - 1)

45/ 3 = n - 1

15 = n-1

n = 15 +1

n = 16