1.tentukan empat suku pertamanya dan suku ke-25 jika suatu barisan memiliki pola suku ke-n berikut a. Un =3n-7 b. Un= 2² + 3n 2.dari deret aritmatika diketauhi

1.a
U1 = 3.1 - 7 = -4
U2 = 3.2 - 7 = -1
U3 = 3.3 - 7 = 2
U4 = 3.4 - 7 = 5

U25 = 3.25 - 7 = 75 - 7 = 68

2.b
U1 = 2² + 3.1 = 7
U2 = 2² + 3.2 = 10
U3 = 2² + 3.3 = 13
U4 = 2² + 3.4 = 16

U25 = 2² + 3.25 = 4 + 75 = 79

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2.
U5 = a + 4b = 5
U10 = a + 9b = 15
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-5b = - 10
b = -10/-5
b = 2

a + 4b = 5
a + 4.2 = 5
a + 8 = 5
a = 5 - 8
a = -3

U10 = a + 9b = -3 + 9.2 = -3 + 18 = 15

S10 = 10/2(-3 + 15) = 5.12 = 60

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U2 = a + b = 5
U4 + U6 = a + 3b + a + 5b = 28

a + b = 5
2a + 8b = 28

a + 4b = 14
a + b = 5
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3b = 9
b = 9/3
b = 3

a + b = 5
a + 3 = 5
a = 5 - 3 = 2

U9 = a + 8b = 2 + 8.3 = 2 + 24 = 26

semoga membantu

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