maths questions

[匿名]

2007-11-03 10:03 am

Q1. 2 2 2 2 2 2 2 2 2 2
(30 －29 )＋(28 －27 )＋(26－25 )＋...＋(4 －3 )＋(2 －1 )

2. It is given that 1/a-2b+1/c=c .
a) Change the subject of the formula to a.

Simplify the following.
1 /x-4 - x/ (4-x)(4-x)

Thank you so much!!

更新1:

Q1. 2 2 2 2 2 2 2 2 2 2 (30 －29 )＋(28 －27 )＋(26－25 )＋...＋(4 －3 )＋(2 －1 )

更新2:

Ans.Q.2 a = c/(c^2-1)+2b and -4/(x-4)^2 Thank you so much!

更新3:

Q1. (30^2 －29^2 )＋(28^2 －27^2)＋(26^2－25^2)＋...＋(4^2－3 ^2)＋(2^2 －1 ) Please help me,too.

回答 (1)

R Ho

2007-11-03 10:52 am

✔ 最佳答案

(1) We have 30 integers grouped into 15 pairs of 2 numbers each. The difference of each pair is always equal to 1, thus the sum of the entire series is 15*1=15.
(2) 1/a-2b+1/c=c
=>1/a = c-1/c+2b
=>1/a = (c^2 - 1)/c + 2b
=> 1/a = (c^2 - 1 + 2bc)/c
thus, a = c/(c^2-1+2bc)
(3) 1 /x-4 - x/ (4-x)(4-x)
=(1/x-4) + x/(x-4)(4-x)
=(1/x-4)[1+x/(4-x)]

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