数学题速求18、19!要过程!

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数学题速求18、19!要过程!

数学题速求18、19!要过程!
数学题速求18、19!要过程!

 

数学题速求18、19!要过程!
18,
= (4+0.4)+(-0.1)+(8+1/3)-(11+2/3)+(1+1/3)
= (4+8-11+1)+(0.4-0.1)+(-2/3+1/3)
=2+3/10-1/3
=1+(30+9-10)/30
=1+29/30
19,
=(1-2)-(3-4)+(5-6)-(7-8)+(9-10)-(11-12)+...+(2009-2010)
=-1-(-1)+(-1)-(-1)+(-1)-(-1)+...+(-1)
=[-1-(-1)]+[(-1)-(-1)]+[(-1)-(-1)]+...+[(-1)]
=-1

18,
= (4+0.4)+(-0.1)+(8+1/3)-(11+2/3)+(1+1/3)
= (4+8-11+1)+(0.4-0.1)+(-2/3+1/3)
=2+3/10-1/3
=1+(30+9-10)/30
=1+29/30

19,
=(1-2)-(3-4)+(5-6)-(7-8)+(9-10)-(11-12)+...+(...

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18,
= (4+0.4)+(-0.1)+(8+1/3)-(11+2/3)+(1+1/3)
= (4+8-11+1)+(0.4-0.1)+(-2/3+1/3)
=2+3/10-1/3
=1+(30+9-10)/30
=1+29/30

19,
=(1-2)-(3-4)+(5-6)-(7-8)+(9-10)-(11-12)+...+(2009-2010)
=-1-(-1)+(-1)-(-1)+(-1)-(-1)+...+(-1)
=[-1-(-1)]+[(-1)-(-1)]+[(-1)-(-1)]+...+[(-1)]
=-1

收起

18 = 4.4+(-0.1)+8.333+1.333+(-11.666)
= 4.3 + (-2)
=2.3
19 = [(1-2)+(-3+4)]+[(5-6)+(-7+8)]+。。。[2009-2010]
= [(-1)+1]+[(-1)+1]+。。。。。(-1)
= -1