Question

Hasil dari 61+58+55...+19+16 adalah?

Answer 1

61 + 58 + 55 + ... + 19 + 16 = ?
Deret aritmatika
a = 6
b = 58 - 61 = - 3

Cari n dari 16

Un = a + (n-1)b
16 = 61 + (n-1)-3
16 = 61 - 3n + 3
16 = 64 - 3n
3n = 64-16
3n = 48
n = 16

Sn = n/2 ( a + Un)
S16 = 16/2 ( 61 + 16)
S16 = 8(77)
S16 = 616

Answer 2

61 + 58 + 55 + ... + 19 + 16

~beda = b = U2 - U1 = 58-61 = -3
~suku awal = a = 61

Un = a + (n-1)b
16 = 61 + (n-1)(-3)
16 = 61 + -3n + 3
16 = 64 - 3n
48 = 3n
16 = n

Sn = n/2 (a+Un)
S16 = 16/2 (61 + 16)
S16 = 8 (77)
S16 = 616