Ada yang tau cara cepetnya?

Bab Baris dan Deret

n = 1
U1 = (-1)^1 × (3(1) + 7)
U1 = -1(10)
U1 = -10

n = 2
U2 = (-1)^2 × (3(2) + 7)
U2 = 1 × (6 + 7)
U2 = 13

n = 3
U3 = (-1)^3 × (3(3) + 7)
U3 = -1 × (9 + 7)
U3 = -16

n = 50
U50 = (-1)^50 × (3(50) + 7)
U50 = 1 × (150 + 7)
U50 = 157

-10 + 13 - 16 + 19 - ... + 157 = 3 + 3 + 3 + ... + 3 [25 kali]

Nilai dari notasi sigmanya adalah
3 × 25 = 75