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a fost răspuns

3+5+7+...........+99
4+6+8+..........+100

Răspuns :

Spidie
3+5+7+...+99=102*49/2=2499
a₂=2*1+1
a₃=2*2+1
a⁴=2*3+1
an=2*x+1
99=2x+1
2x=98
x=49


4+6+8+..........+100 = 2*(2+3+4+...50)=2*50*51/2 - 2= 2549


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