tolong dijawab ya sama jalannya mau dikumpol besok ...please

U8=4 dan U3=9
jawaban a
(8-3)b = 4-9
5b=-5
b=-1

U3=9
a+2b=9
a+2(-1) = 9
a=9+2
a=11
jawaban b
Un = a+(n-1)b
=11+(n-1)(-1)
=11-n+1
=12-n
jawaban c
U1001 = 12 - 1001
=-989
jawaban c
S1001 = (1001/2)(11+(-989)
= (1001/2)(-978)
=1001 . (-489)
=-489489