tolong di bantu ya,kasih jwbn yg bnr jngn boong .

4) a = 20
b = 24 - 20 = 4
n = 25
Sn = ½ • n ( 2a + ( n - 1 )b )
S25 = ½ • 25 ( 2(20) + ( 25 - 1)4)
= 25/2 ( 40 + 96)
= 25/2 • 136
= 1.700

5) a = 7
b = 4
Un = a + ( n - 1)b
103 = 7 + ( n - 1) 4
103 = 7 + 4n - 4
103 = 3 + 4n
103 - 3 = 4n
4n = 100
n = 25
S25 = ½ • 25 ( a + U25)
= 25/2 ( 7 + 103)
= 25/2 • 110
= 1.375 ( B )

7) U5 = a + 4b = 8
U9 = a + 8b = 20
---------------------------(-)
- 4b = - 12
b = 3
a + 4b = 8
a + 4(3) = 8
a + 12 = 8
a = 8 - 12
a = - 4
U10 = a + 9b
= - 4 + 9(3)
= - 4 + 27
= 23