问两个算式的解答1.1-2+3-4+5-6+.+1989-1990+1991=(有过程)2.(99*99+98*98+...90*90)-(89*89+88*88...+80*80)=(有过程)短点
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![问两个算式的解答1.1-2+3-4+5-6+.+1989-1990+1991=(有过程)2.(99*99+98*98+...90*90)-(89*89+88*88...+80*80)=(有过程)短点](/uploads/image/z/12877590-30-0.jpg?t=%E9%97%AE%E4%B8%A4%E4%B8%AA%E7%AE%97%E5%BC%8F%E7%9A%84%E8%A7%A3%E7%AD%941.1-2%2B3-4%2B5-6%2B.%2B1989-1990%2B1991%3D%28%E6%9C%89%E8%BF%87%E7%A8%8B%292.%2899%2A99%2B98%2A98%2B...90%2A90%29-%2889%2A89%2B88%2A88...%2B80%2A80%29%3D%28%E6%9C%89%E8%BF%87%E7%A8%8B%29%E7%9F%AD%E7%82%B9)
问两个算式的解答1.1-2+3-4+5-6+.+1989-1990+1991=(有过程)2.(99*99+98*98+...90*90)-(89*89+88*88...+80*80)=(有过程)短点
问两个算式的解答
1.1-2+3-4+5-6+.+1989-1990+1991=(有过程)
2.(99*99+98*98+...90*90)-(89*89+88*88...+80*80)=(有过程)
短点
问两个算式的解答1.1-2+3-4+5-6+.+1989-1990+1991=(有过程)2.(99*99+98*98+...90*90)-(89*89+88*88...+80*80)=(有过程)短点
1-2+3-4+5-6+7-.+1989-1990+1991
=(1-2)+(3-4)+(5-6)+(7-8)+.+(1989-1990)+1991
=-1-1-1-1-.-1+1991
=-1*(1990/2)+1991
=-995+1991
=996
(99*99+98*98+...90*90)-(89*89+88*88...+80*80)
=(99*99-89*89)+(98*98-88*88)+...+(91*91-81*81)+(90*90-80*80)
=(99+89)*(99-89)+(98+88)*(98-88)+...+(91+81)*(91-81)+(90+80)*(90-80)
=(99+89)*10+(98+88)*10+...+(91+81)*10+(90+80)*10
=10*[99+98+...+91+90+89+88+...+81+80]
=10*[(99+81)+(98+82)+...+(91+89)+(90+80)]
=10*[180+180+...+180+170]
=10*[180*9+170]
=10*[180*9+(180-10)]
=10*[180*9+180-10]
=10*[(180)*(9+1)-10]
=10*1800-100
=18000-100
=17900