tolong ya no 4 (a .b .c)

A. 1 +3 +5 +7 +9
99+97 +95 +93 +91
=100+100+100+100+100
=100×50÷2=250
B. 1-2 +3-4 +5-6 +7-8 +... 100
(1-2) + (3-4)+ (5-6) + (7-8)+... (99-100)
= -1 + -1 + -1 + -1 +... -1
= -1×50= -50
c. bilangan negatif=
-100-99-98...-2 -1
-1 -2 -3 ...-99-100
=-101-101-101..-101-101
= -101×100÷50= -5050
Bilangan positif=
1 +2 +3 +4+... +50
50+49+48+47... +1
=51 +51 +51+51... +51
=51×50÷2=1275
bilangan negatif+bilangan positif
= -5050 + 1275
= -3775