Question

An arithmetic sequence is known as U4 = 23 and U9 = 48. the number of the first 10 tribes is ...

Answer 1

Known :

U4 = 23

U9 = 48

Asked: S10

b = (U9 - U4) / (9 - 4)

b = (48 - 23) / 5

b = 25/5

b = 5

a = U4 - 3b

a = 23 - 3.5

a = 23-15

a = 8

The first 10 tribes

Sn = n / 2 (2a + (n - 1) b)

S10 = 10/2 (2.8 + (10-1) 5)

S10 = 5 (16 + 45)

S10 = 5 (61)

S10 = 305

Hope it helps ✌

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Mapel = Mathematics

Class = 8 Middle School

Material = Rows and Series

Keywords = Arithmetic sequence, Sn

Answer 2

known:

U4 = 23

U9 = 48

U9 = a + (9-1) b

U4 = a + (4-1) b

substitution

a + 8b = 48

a + 3b = 23

_______ _

5b = 25

b = 25

__

5

b = 5

a = ...?

a + 8b = 48

a + 8 × 5 = 48

a + 40 = 48

a = 48-40

a = 8

formula = sn = n / 2x (2a + (n-1) b

U10 = 10 / 2x (2x8 + (10-1) 5

= 5x (16+ (5-50)

= 5x (16 + 45)

= 5x61

= 305

I hope this helps