Tính và tìm x,y,z

N

nguyenbahiep1

câu 1

[laTEX]\frac{n^2}{(2n-1)(2n+1)} = \frac{1}{8}(2 + \frac{1}{2n-1} - \frac{1}{2n+1}) \\ \\ \frac{1^2}{1.3} = \frac{1}{8}( 2 + \frac{1}{1} - \frac{1}{3}) \\ \\ \frac{2^2}{3.5} = \frac{1}{8}( 2 + \frac{1}{3} - \frac{1}{5}) \\ \\ ......................\\ \\ \frac{1005^2}{2009.2011} = \frac{1}{8}( 2 + \frac{1}{2009} - \frac{1}{2011}) \\ \\ \Rightarrow E = \frac{1}{8}( 2.1005 + 1 - \frac{1}{2011}) = ?[/laTEX]
 
P

perfectday8

$ 2) \ pt \leftrightarrow (3x - 5)(1+yz) +3z = 0 \\
\rightarrow x < \frac{5}{3} \rightarrow x = 1 \\
pt \leftrightarrow -2 -2yz +3z = 0 \leftrightarrow (3-2y)z = 2 \leftrightarrow z = 2 \vee 3-2y = 1 \leftrightarrow y = 1. $
 
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