suku ke 2=6 dan suku ke 10=22 jumlah 20 sukupertama adalah,pakai caranya

U2 = a + b = 6
U10 = a + 9b = 22
______________
-8b = -16
b = 2

a + b = 6
a + 2 = 6
a = 4

S20 = n/2 (2a + 19b)
S20 = 20/2 (2(4) + 19(2))
S20 = 10 (8 + 38)
S20 = 10 (46)
S20 = 460

Semoga Membantu

Materi : Barisan dan deret

Pembahasan :
Beda = (U10 - U2)/(10 - 2)
Beda = (22 - 6)/8
Beda = 16/8
Beda = 2

U2 = 6
a + b = 6
a + 2 = 6
a = 4

U20 = a + 19b
U20 = a + 9b + 10b
U20 = 22 + 10(2)
U20 = 22 + 20
U20 = 42

Maka...
Sn = n/2(a + Un)
S20 = 20/2(4 + U20)
S20 = 10(4 + 42)
S20 = 10(46)
S20 = 460