diket barisan aritmatika u3=14,u7=26 tentukan u15

BARISAN ARITMATIKA
U3 = a+2b = 14
U7 = a+6b= 26

U7–U3
(a+6b) – (a+2b) = 26–14
4b = 12
b = 12/4
b = 3

a+2b = 14
a+(2×3) = 14
a+6 = 14
a = 14–6
a = 8

U15 = a+14b
= 8+(14×3)
= 8+42
= 50

Dik : U3 = 14
U7 = 26

Dit : U15 = ?

Un = a + (n-1) b

U3 = a + (3-1) b
14 = a + 2b

U7 = a + (7-1) b
26 = a + 6b

Eliminasi a sehingga diperoleh b :
a + 6b = 26
a + 2b = 14
------------------ -
4b = 12
b = 12/4
b = 3

subtitusi :
14 = a + 2b
14 = a + 2(3)
14 = a + 6
14 -6= a
8 = a



Un = a + (n-1) b
U15 = 8 + (15-1) 3
= 8 + 14(3)
= 8 + 42
= 50



maaf klo salah