U3 = 3 U9= 45 berapa U40

U3 = a+2b=3
u9 = a+8b=45
--------------- (-)
-6b = -42. b = 7
a + 2b=3
a+2(7)=3
a+14=3
a=-11

U40 = a+39b
u40 = -11 + 39(7) = 262

Un = a + (n-1)b
U40 = a + (40-1)b
= a + 39b
Mencari a & b :
U3 = a + (3-1)b U9 = a + (9-1)b
3 = a + 2b 45= a + 8b

Eleminasi : Subtitusi :
a + 2b = 3 a + 2b = 3
a + 8b = 45 - a + 2(7) = 3
-------------------- a = 3 - 14
-6b = -42 a = -11
b = 7
U40 = a + 39b
= -11 + 39(7)
= 262