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Calculați urmatoarele sume a) 2+4+6+8+...+200 b) 5+10+15+20+...+250

Răspuns :

a) 2+4+6+..+200=

= 2(1+2+3+..+100)= 2[tex]\frac{100x101}{2}[/tex]= 100x101=10100

b) 5+10+15+..+250=

=5(1+2+3+..+50)= 5[tex]\frac{50x51}{2}[/tex]= 5x25x51=125x51=..