Question

tolong jawab pakai cara, makasih!!

Answer 1

8) a = 1
r = 2
S6 = 1 x (2^6 - 1)/(2-1) = 64-1/1 = 63

9) U2 = 50 ,,,, u6 = 30
b = (30-50)/(6-2) = -20/4 = -5
U2 = a + b
50 = a - 5
a = 55
Un = 55 + 5 - 5n = 60 - 5n
U30 = 60 - 5x30 = -90
S30 = 15 x ( 55 - 90) = 15 x (-35) = -525

10) a = 3
b = 2
Un = 2n + 3 - 2 = 2n + 1
U7 = 2x7 + 1 = 15

Answer 2

8. Sn = a (r^n - 1) / r - 1
Sn = 1 (2^6 - 1)/ 2-1
Sn = 1 (64-1)/1
S6 = 1 (63)/1
S6 = 63

9. U2 = 50
U6 = 30
S20 = ?

• Un = a + (n-1) b

U2 = a + (2-1) b (i)
U6 = a + (6-1) b (ii)
50 = a + b
30 = a + 5b
------------------ -
-4b = 20
b = -5

a + b = 50
a + (-5) = 50
a = 50 - (-5)
a = 55

Sn =  n/2 x { 2a + (n-1) x b}
S20 = 20/2 x { 2 x 55 + (20-1) x (-5)}
S20 = 10 x {110 + 19 x (-5)}
S20 = 10 x {110 + -95}
S20 = 10 x 15
S20 = 150

10. a = 3
b = 2
Un = a + (n-1) b
U7 = 3 + (7-1)2
U7 = 3 + (6) 2
U7 = 3 + 12
U7 = 15