diletahui u4 =10 dan u8=30 . carilah nilai dari u 50 dan S50

Materi : Barisan Dan Deret
Kelas : IX SMP

U4 = U1 + 3b = 10
U8 = U1 + 7b = 30
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=======> -4b = -20
=======> b = 5

U4 = U1 + 3b
U1 = U4 - 3b
U1 = 10 - 3(5)
U1 = 10 - 15
U1 = -5

U50 = U1 + 49b
U50 = -5 + 49(5)
U50 = -5 + 245
U50 = 240

Sn = n/2 (2.U1 + (n - 1) b)
S50 = 50/2 ( 2(-5) + 49(5))
S50 = 25 ( -10 + 245 )
S50 = 25 ( 235 )
S50 = 5.875