barisan dan deret 1. 20, 26, 32,... tentukan U5, U7, S5, S7 2. 3, 12, 48,... tentukan U4, U8, S4, S6

1.
rumus Un = a + (n-1) .b
rumus Sn= 1/2 n (2.a + (n-1) . b)
u5= 20 + (5-1) . 6 =44
u7= 20 + (7-1)  . 6 = 56
s5= 1/2 5 ( 2.20 + (5-1) . 6) = 115
s7= 1/2 7 (2.20 + (7-1) . 6 )= 266
2. 
u4= 2 + (4-1) . 1 = 5
u8= 2 + (8-1) .1 = 9
s4= 1/2 4 (2.2 + (4-1) . 1) = 14
s6= 1/2 6 (2.2 + (6-1) .1) = 27

1. a = 20
    b = 4
Un = a + (n-1)b
U₅ = 20 + 4(6))
     = 46

U₇ = 20 + 6(6)
     = 56

Sn = n/2 (U₁ +  Un)
S₅ = 5/2 (20 + 46)
     = 5/2 (66)
     = 165 

S₇ = 7/2 (20 + 56)
     = 7/2 (76)
     = 266

2. a = 3
    r = 4

Un = a(r)^n-1
U₄ = 3(4)⁴⁻¹
     = 3(4)³
     = 3(64)
     = 192

U₈ = 3(4)⁸⁻¹
     = 3(4)⁷
     = 3(16384)
     = 49152

Sn = a(r^n - 1) / r - 1
S₄ = 3(4⁴ - 1) / 4 - 1
     = 3(256) / 3
     = 256 

S₆ = 3(4⁶ - 1) / 6 - 1
     = 3(4095) / 5
     = 2457