Suatu barisan aritmatika diketahui U5=21 dan U10=41 maka tentukan besar U16!

Un = a + ( n - 1 ) b

U5 = a + 4b = 21
U10 = a + 9b = 41
--------------------------(-)
- 5b = - 20
b = 4

subtitusi
a + 4b = 21
a + 4(4) = 21
a + 16 = 21
a = 21 - 16
a = 5

U16 = a + 15b
= 5 + 15(4)
= 5 + 60
= 65

U5=a+4b=21
U10=a+9b=41
-------------------- -
-5b=-20
b=-20/-5
b=4

a+4b=21
a+4(4)=21
a+16=21
a=21-16
a=5

U16=a+(n-1)b
=5+15x 4
=5+60
=65