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1²-2²= 1-4=-3
3²-4²= 9-16=-7
5²-6²= 25-36= -11
a²-b²= -1x(a+b)
-1 ( 3+7+11+15+...+4031)
U 1/a= 3
b=7-3= 4
Un= a+(n-1)b
4031= 3+(n-1)4
4031= 3+4n-4
4031+1= 4n
4032=4n
n=4032/4
n=1008
Sn= n/2(2a+(n-1)b
= 1008/2 (2(3)+(1008-1)4)
= 504(6+(1007(4))
= 504(6+4028)
= 504 x 4034
= 2.033.136
-Sn= -2.033.136
... maaf kalau ada yg salah