39²= (40-1)²=40²-2×1×40+1²=1600-80+1=1521
999²= (1000-1)²=1000²- 2•1•1000+1²=1000000-2000+1=998001
31²= (30+1)²=30²+60+1=961
103²= (100+3)²=100²+600+9=10609
1001²= (1000+1)²=1000000+2000+1=1002001
51²= (50+1)²=2500+100+1=2601
99²= (100-1)²=10000 -200+1=9801
105²= (100+5)²=10000 +1000+25=11025
39²= (40-1)²=40²-2×1×40+1²=1600-80+1=1521
999²= (1000-1)²=1000²- 2•1•1000+1²=1000000-2000+1=998001
31²= (30+1)²=30²+60+1=961
103²= (100+3)²=100²+600+9=10609
1001²= (1000+1)²=1000000+2000+1=1002001
51²= (50+1)²=2500+100+1=2601
99²= (100-1)²=10000 -200+1=9801
105²= (100+5)²=10000 +1000+25=11025