suatu deret aritmatika memiliki nilai suku ke-3 dan suku ke 7 berturut-turut 14 dan 26. jumlah 20 suku pertama deret tersebut adalah.. sama cara nya ya kak ,, b

langsung aja y

U3 = a + 2b = 14
U7 = a + 6b = 26
_____________-
-4b = -12
b = 3

a + 2b = 14
a = 14 - 2(3)
a = 14 - 6
a = 8

S20 = 20/2 (2a + 19b)
S20 = 10 (2.8 + 19.3)
S20 = 10 (16+57)
S20 = 10 (73)
S20 = 730

semoga berguna +_+

U3 = U1 + 2b = 14
U7 = U1 + 6b = 26
-----------------------------[-]
========> -4b = -12
========> b = 3

U3 = U1 + 2b
14 = U1 + 2.3
14 = U1 + 6
U1 = 14 - 6
U1 = 8

Sn = n/2 ( 2.U1 + (n-1)b)
S20 = 20/2 ( 2.8 + (20-1) 3)
S20 = 10 ( 16 + 19.3)
S20 = 10 ( 16 + 57 )
S20 = 10 (73)
S20 = 730

semoga membantu