dik barisan aritmatika u3=18 dan u2=38 tent suku ke 10

a+2b=18
a+b=38
b=-20 a=58
U10=a+9b
= 58+9(-20)
=58+(-180)
=-122

u1= a
u2= a+b
u3=a+2b

38= a+b
18= a+2b
_________-
20= -b
b= -20

u2= a+b
38= a-20
38+20= a
a= 58

un= a+(n-1)b
un= 58+(n-1)(-20)
un= -20n+20+58
un= -20n+78

u10= -20n+78
u10= -20(10)+78
u10= -200+78
u10= -122