jika 1 + 3 + 5 + ..... + n = 100, maka n bernilai ....

Deret Aritmatika


a = 1
b = 3-1 = 2
Un = x (spy ga ad kerancuan , aku pake x aja)
Sn = 100

x?

Sn = n/2 ( 2a + (n - 1)b)
100 = n/2 ( 2.1 + (n - 1)2)
100 = n/2 ( 2 + 2n - 2)
100 = n/2 ( 2n)
100 = n²
n = 10

Maka U10 = x
a + 9b = x
1 + 9.2 = x
1+18 = x
x = 19

krn x pengganti n

maka
n = 19

Sn = n/2(2a + (n-1)b) 
b = 2
a = 1 
-> 100 =n/2( 2(1) + ( 2n - 2 ))
100 = n(2n)/2
100 = 2n'2/2
100 = n'2
n = 10  

U10 = a + (9)2 
u10 = 1 + 18
u10 = 19 

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