Question

Hitunglah jumlah dari deret aritmatika berikut, 2+7+12....302

Answer 1

A = 2
b = U₂ - U₁
   = 7 - 2
   = 5
Un = 302

Un = a + (n - 1)b
302 = 2 + (n - 1)5
302 = 2 + n(5) - 1(5)
302 = 2 + 5n - 5
302 = 5n - 3
302 + 3 = 5n
305 = 5n
305/5 = n
61 = n
n = 61

Sn = n/2(2a + (n - 1)b)
S₆₁ = 61/2(2(2) + (61 - 1)5)
       = 61/2(4 + (60)5)
       = 61/2(4 + 300)
       = 61/2(304)
       = 18544/2
       = 9272

semoga benar yaaaa