Question

Find the sum of the series -5+(-8)+(-11)+........+(-230) ?

Answer 1

It is an A.P.,

in which, a= -5, d= -8-(-5)=-3, l=-230

First calculate the number in series.....

l=a+(n-1)d

-230=-5+(n-1)-3

-225=-3n + 3

3n=228

n=76.

Now,

Sum of the series  = n/2 (a+l)

  76/2 (-5-230)

38 * -235  = -8930.

So, the sum of your series would be -8930.

Answer 2

Answer:

-8930

Step-by-step explanation:

a= -5

d= -3

∵an= -230 (last term)

an= a+(n-1)d

-230=-5+(n-1)-3

-230= -5-3n+3

-230= -2-3n

-230+2= -3n

-228= -3n

n= -228/-3

∴n= 76

∵sn = n/2(2a+(n-1)d)

s76= 76/2{2(-5)+(76-1)(-3)}

s76=38{-10-225}

s76=38×(-235)

s76 = -8930

sum of the numbers is  -8930

hope its helpful to you

i did it with different formula i.e sn = n/2{2a+(n-1)d]

instead of sn=n/2(a+l)