Question

11+9+7+........n terms =-13 then the value of n is

Answer 1

Answer:

n = 13

Step-by-step explanation:

11+9+7+........n terms =-13

a = 11

d = -2

Sum of n term = (n/2)(first term + nth term)

(n/2)(a + a +(n-1)d) = -13

n(11 + 11 + (n-1)(-2)) = -26

n(22 -2n +2) = -26

24n - 2n² = -26

12n - n² = -13

n²-12 - 13 = 0

n² -13n + n -13 = 0

n(n-13) +1 (n-13) = 0

(n+1) (n-13) = 0

n = 13   as n can not be negative

Answer 2

Answer:

Step-by-step explanation:

Simple method

The answer is 13