tentukan U9 jika diketahui U3 = 32 U5 = 8

U3= a+2b = 32
U5= a+4b = 8
                             -
          -2b = 24
             b = 24:-2
             b = -12

B=-12 => a+2b=32
           a+2(-12)=32
             a+(-24)=32
                        a=32+24
                        a=56

Un= a+(n-1)b
U9= 56+(9-1)-12
    = 56+(8)-12
    = 56+(-96)
    = -40

Jadi U9=-40