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2014-10-29T20:53:26+02:00
A) a=(1+2+3+...+99)×2+100 =(99x100:2)x2+100=4950x2+100=9900+100=1000=100²
B) a=1+2+3+...+50-25×50=(50x51:2)-25x50=1275-1250=25=5²
C) a=3+6+9+...+75-75
=3x(1+2+3+...+25)-75=3x(25x26:2)-75=3x325-75=975-75=900=30²
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