Question

Itu merupakan soal aritmatika teman teman.
Trimakasih atas partisipasinya.

Answer 1

Verified answer

U5 = a + (5-1)b
 255 = a + 4b

U8 = a + (8-1)b
210 = a + 7b

a + 7b = 210
a + 4b = 255
---------------------- -
      3b = -45
        b = -15

a + 4b = 255
a + 4(-15) = 255
a - 60 = 255
a = 255 + 60 = 315

Un = a + (n - 1)b
0 = 315 + (n - 1)-15
0 = 315 - 15n + 15
0 = -15n + 330
15n = 330
n = 22

Answer 2

Verified answer

Un = a + (n - 1) × b
U₅ = 255 → 255 = a + (5 - 1) × b → 255 = a + 4b ...pers1
U₈ = 210 → 210 = a + (8 - 1) × b → 210 = a + 7b ...pers2

Eliminasi pers1 dan pers2
a + 4b = 255
a + 7b = 210
___________-
-3b = 45
b = 45 ÷ (-3)
b = -15

a + 4b = 255
a + 4(-15) = 255
a - 60 = 255
a = 255 + 60
a = 315

Un = 0
n = ?

a + (n - 1) × b = 0
315 + (n - 1) × (-15) = 0
315 - 15n + 15 = 0
330 - 15n = 0
15n = 330
n = 330 ÷ 15
n = 22