dik u3=9 u7=21 tentukan beda,u1 dan u15

U3 = 9
U7 = 21
Un = a + (n-1)b

U3 = a + 2b = 9
U7 = a + 6b = 21
_____________ _
-4b = -12
b = -12/-4
b = 3

Lalu, kita ambil salah satu persamaan :
a + 2b = 9
a + 2(3) = 9
a = 9 - 6
a = 3

U15 = a + 14b
U15 = 3 + 14(3)
U15 = 3 + 42
U15 = 45

Semoga membantu :)

▶MAPEL : MATEMATIKA

▶KELAS : IX

▶BAB : BARISAN & DERET
----------------------------------------


Diketahui :
↪U3 = 9
↪U7 = 21

Ditanya :
↪beda barisan
↪U1 (a)
↪U15


Jawaban :
==========

→ Beda barisan

U7 - U3 = 21 - 9

7b - 3b = 12

4b = 12

b = 12/4

b = 3 ✔


→ Suku Pertama (a)

U3 = 9

a + (3-1)b = 9

a + 2(3) = 9

a + 6 = 9

a = 9 - 6

a = 3 ✔



→ Suku ke 15

U15 = a + (n-1)b

U15 = 3 + (15-1)(3)

U15 = 3 + 14(3)

U15 = 3 + 42

U15 = 45 ✔