Question

if d= -2, a=100, an = -10, find Sn

Answer 1

it is very simple bro...
-10=a+(n-1)d
-10=100+(n+2d)
-110=n+2n
n=55(n-1)
n=55+1=56
Answer...

Answer 2

HLO MATE ✋✋
Simran Here !!!!

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Given That :
a = 100
an = - 10
d = -2
Sn = ?

First we have to find the number of terms (n)
an = a+(n-1)d
-10 = 100 + (n-1) -2
-10 - 100 = (n-1) -2
-110 = (n-1) -2
-110/-2 = (n-1)
55 = (n-1)
n = 55+1
n = 56

⏩So,Number of terms (n) is 56✔

NOW ,
Sn = n/2 [2a + (n-1)d]
Sn = 56/2 [2×100+ (55) -2]
Sn = 28 [200 - 110]
Sn = 28 [90]
Sn = 2520

⏩So , Sum of Number of terms is 2520✔✔
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HOPE IT HELPS UH ☺
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