tolong dijawab 1.tentukan jumlah sesuai yang diminta dari setiap deret berikut : a) 4+7+10+13+.... (S36) b)27+23+19+15+.... (S24) c)7+1-5-13-....

Nomer 1

a ) a = 4 dan b = 3

Sn = ½n(2a+(n-1)b)
S36 = 18 ( 8 + 105 )
S36 = 2.034

b ) a = 27 dan b = -4

Sn = ½n(2a+(n-1)b)
S24 = 12 ( 54 - 92 )
S24 = -456

c ) a = 7 dan b = -6

Sn = ½n(2a+(n-1)b)
S15 = 7½ ( 14 - 84 )
S15 = -450

d ) a = 8 dan b = ¼

Sn = ½n(2a+(n-1)b)
S17 = 8½ ( 16 + 4 )
S17 = 170

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Nomer 2.

a ) a = 2 dan b = 2

Un = a+(n-1)b
100 = 2+2n-2
100 = 2n
n = 50

Sn = ½n(2a+(n-1)b)
S50 = 25 (4+98)
S50 = 2.550

b ) a = 4 dan b = 3

Un = a+(n-1)b
103 = 4+3n-3
103 = 3n+1
102 = 3n
n = 34

Sn = ½n(2a+(n-1)b)
S34 = 17 (8+99)
S34 = 1.819

c) a = 15 dan b = -6

Un = a+(n-1)b
-75 = 15-6n+6
-75 = -6n+21
-96 = -6n
n = 16

Sn = ½n(2a+(n-1)b)
S16 = 8 (30-90)
S16 = -480

d ) a = -32 b = 4

Un = a+(n-1)b
32 = -32+4n-4
32 = 4n-36
68 = 4n
n = 17

Sn = ½n(2a+(n-1)b)
S17 = 8½ (-64+64)
S17 = 0

Semoga bermanfaat