Tentukanlah jumlah 8 suku pertama dari masing” deret di bawah ini A. -2,-4,-6,-... B.-3+4+11+....

a.)

a = -2

b = U2 - U1
b = -4 - (-2)
b = -4 + 2
b = -2

Sn = n/2 ( 2a + ( n - 1 ) b )
S₈ = 8/2 ( 2(-2) + ( 8 - 1 ) -2 )
S₈ = 4 ( -4 + 7(-2) )
S₈ = 4 ( -4 + (-14) )
S₈ = 4 ( - 4 - 14 )
S₈ = 4 ( -18 )
S₈ = -72

b.)

a = -3

b = U2 - U1
b = 4 - (-3)
b = 4 + 3
b = 7

Sn = n/2 ( 2a + ( n - 1 ) b )
S₈ = 8/2 ( 2(-3) + ( 8 - 1 ) 7 )
S₈ = 4 ( -6 + 7(7) )
S₈ = 4 ( -6 + 49 )
S₈ = 4 ( 43 )
S₈ = 172

[tex]~[/tex]

a. Sn = S/2 (2a + (n-1)b
S8 = 8/2 (2.-2+(7)-2
S8 = 4 (-4-14)
S8 =4 × (-18) = -72

b S8 = 8/2 (2.-3 + (7)7
S8 = 4 × 43
S8= 172