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5+10+15+20+....+1000=
8+16+24+32+...+4000=


Răspuns :

5+10+15=20+...+1000=
=5(1+2+3+...+200)=
=5x200x201:2=
=5x100x201=
=500x201=
=100500

a) 5×(1+2+3+...+200)=
S=200×201÷2
S=20100
5×20100=100500
b) 8×(1+2+3+...+500)
S=500×501÷2
S=125250
8×125250=1,002,000