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ex5: calculate 2+4+6+........+100-(1+3+5+........+99)=..........

Răspuns :

2+4+6+........+100-(1+3+5+........+99)=2*(1+2+3+4+...50) - (1+3+5+...99)=

= 2*50*51/ 2-  50² = 2550-2500=50