1/1×2+1/2×3+1/3×4+…… +1/2005×2006+1/2006×2007+1/2007×2008

1/1×2+1/2×3+1/3×4+…… +1/2005×2006+1/2006×2007+1/2007×2008

1/1×2+1/2×3+1/3×4+…… +1/2005×2006+1/2006×2007+1/2007×2008
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+…… +(1/2005-1/2006)+(1/2006-1/2007)+(1/2007-1/2008)
=1-1/2+1/2-1/3+1/3-1/4+…… +1/2005-1/2006+1/2006-1/2007+1/2007-1/2008
Intermediate offset
=1-1/2008
=2007/2008

2006 by 20072007-2007 by 20062006 =?

2006*20072007-2007*20062006
=2007*20072007-2007*20062006-20072007
=2007*(20072007-20062006)-20072007
=2007*10001-20072007
=20072007-20072007
=0

Simple calculation of 2006 * 20072007-2007 * 20062006

2006*20072007-2007*20062006=2006×(2007×10001)-2007×(2006×10001)=0

Grade 6 math problems! Only 3! Urgent! Online and so on!
1. For a project, it takes 10 days for team a to complete it alone, and 15 days for team B to complete it alone. If the two teams cooperate, the work efficiency will be reduced. Team a can only complete four fifths of the original, and team B can only complete nine tenths of the original. Now it takes eight days to complete the project, how many days will the two teams cooperate at least?
These two questions all need to be listed!
Don't use equations unless you have to
Answer as many as you can
Thank you!
If a bamboo pole is less than 6m long, measure it from one end to 3m and make a number a, then measure it from the other end to 3m and make a number B. at this time, the distance of AB is 20% of the total length.

Team a does it alone and completes 1 / 10 every day, team B does it alone and completes 1 / 15 every day, and team B cooperates and completes 1 / 10 * 4 / 5 + 1 / 15 * 9 / 10 = 7 / 50 every day
At least the number of days to cooperate is
（1-8/10）/（7/50-1/10）=5

-3-8 + 6-8 = () a math problem

_ 13 ah, for praise

How many four digit passwords are there?

A total of four digits = 5x5x4x3 = 300 (species) can only be 1,2,3,4,5 in thousand digits; five in hundred digits after removing the number in thousand digits plus 0; one of the remaining four in ten digits, four; one of the remaining three in single digits, three. Therefore, there are 300 species

2006+200.6+20.06+2.006+994+99.4+9.94+0.994=______ ．

2006 + 200.6 + 20.06 + 2.006 + 994 + 99.4 + 9.94 + 0.994 = (1006 + 994) + (200.6 + 99.4) + (20.6 + 9.4) + (2.006 + 0.994), = 3000 + 300 + 30 + 3, = 3333

+2006）-（1+3+5+.+2005）

=2+4+6+.+2006-1-3-5-.-2005
=(2-1)+(4-3)+...+(2006-2005)
=1003

How much is it after 60 seconds? 2. How much is it after 60 seconds
? math problem! Urgent! 1; increase 20000 every 0.85 seconds, how much is it after 60 seconds? 2; increase 30000 every 0.60 seconds, how much is it after 60 seconds? If you know the method, please type it

60÷0.85≈70
20000×70=1400000
60÷0.60=100
30000×100=3000000

2013.11.
1. Find the standard deviation of 2A + 2, 2A + 4, 2A + 6 and 2A + 8
2. If 0 ° ≤ x ≤ 360 °, how many real roots does the equation (cosx + 1) (4sin & # 178; x-1) = 0 have?

In the standard deviation formula, the result is 30. In the second problem (cosx + 1) (4sin & # 178; x-1) = 0, then (cosx + 1) = 0 or (4sin & # 178; x-1) = 0, discuss separately, because 0 °≤ x ≤ 360 °, so for the first discussion, X can be PI (that is 180 degrees), and for the second discussion, SiNx = 1 / 2