Đại số lớp 7

Phạm Đức Minh

tìm x, biết: \(\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+349}{5}=0\)

Lightning Farron
6 tháng 4 2017 lúc 15:22

\(\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+349}{5}=0\)

\(\Leftrightarrow\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+329+20}{5}=0\)

\(\Leftrightarrow\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+329}{5}+\dfrac{20}{5}=0\)

\(\Leftrightarrow\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+329}{5}+4=0\)

\(\Leftrightarrow\dfrac{x+2}{327}+1+\dfrac{x+3}{326}+1+\dfrac{x+4}{325}+1+\dfrac{x+5}{324}+1+\dfrac{x+329}{5}=0\)

\(\Leftrightarrow\dfrac{x+329}{327}+\dfrac{x+329}{326}+\dfrac{x+329}{325}+\dfrac{x+329}{324}+\dfrac{x+329}{5}=0\)

\(\Leftrightarrow\left(x+329\right)\left(\dfrac{1}{327}+\dfrac{1}{326}+\dfrac{1}{325}+\dfrac{1}{324}+\dfrac{1}{5}\right)=0\)

\(\Rightarrow x+329=0\). Do \(\dfrac{1}{327}+\dfrac{1}{326}+\dfrac{1}{325}+\dfrac{1}{324}+\dfrac{1}{5}\ne0\)

\(\Rightarrow x=-329\)

Hương Yangg
6 tháng 4 2017 lúc 15:24

Pt \(\Leftrightarrow\left(\dfrac{x+2}{327}+1\right)+\left(\dfrac{x+3}{326}+1\right)+\left(\dfrac{x+4}{325}+1\right)+\left(\dfrac{x+5}{324}+1\right)+\left(\dfrac{x+349}{5}-4\right)=0\)
\(\Leftrightarrow\dfrac{x+329}{327}+\dfrac{x+329}{326}+\dfrac{x+329}{325}+\dfrac{x+329}{324}+\dfrac{x+329}{5}=0\)
\(\Leftrightarrow\left(x+329\right)\left(\dfrac{1}{327}+...+\dfrac{1}{324}+\dfrac{1}{5}\right)=0\)
\(\Leftrightarrow x+329=0\) ( Vì \(\left(\dfrac{1}{327}+...+\dfrac{1}{324}+\dfrac{1}{5}\right)\ne0\) )
<=> x= -329
Vậy x= -329 là giá trị cần tìm

Nguyễn Nguyệt Hằng
6 tháng 4 2017 lúc 15:32

Ta có:\(\dfrac{x+2}{327}+\dfrac{x+3}{326}+\dfrac{x+4}{325}+\dfrac{x+5}{324}+\dfrac{x+349}{5}=0\)

\(\Rightarrow\left(\dfrac{x+2}{327}+1\right)+\left(\dfrac{x+3}{326}+1\right)+\left(\dfrac{x+4}{325}+1\right)+\left(\dfrac{x+349}{5}-4\right)=0\)

\(\Rightarrow\dfrac{x+329}{327}+\dfrac{x+329}{326}+\dfrac{x+329}{325}+\dfrac{x+329}{5}=0\)

\(\Rightarrow\left(x+329\right)\left(\dfrac{1}{327}+\dfrac{1}{326}+\dfrac{1}{325}+\dfrac{1}{5}\right)=0\)

\(\left(\dfrac{1}{327}+\dfrac{1}{326}+\dfrac{1}{325}+\dfrac{1}{5}\right)\ne0\)

\(\Rightarrow x+329=0\)

\(\Rightarrow x=-329\)

Đào Thanh Huyền
6 tháng 4 2017 lúc 15:33

\(\left(\dfrac{x+2}{327}+1\right)\)+\(\left(\dfrac{x+3}{326}+1\right)\)\(\left(\dfrac{x+4}{325}+1\right)\)\(\left(\dfrac{x+5}{324}_{ }+1\right)\)+\(\left(\dfrac{x+349}{5}-4\right)\)=0

\(\dfrac{x+329}{327}\)+\(\dfrac{x+329}{326}\)+\(\dfrac{x+329}{325}\)+\(\dfrac{x+329}{324}\)+\(\dfrac{x+329}{5}\)=0

(x+329).\(\left(\dfrac{1}{327}+\dfrac{1}{326}+\dfrac{1}{325}+\dfrac{1}{324}+\dfrac{1}{5}\right)\)=0

\(\dfrac{1}{327}\)+\(\dfrac{1}{326}\)+\(\dfrac{1}{325}\)+\(\dfrac{1}{324}\)+\(\dfrac{1}{5}\)\(\ne\)0

=>x+329=0

=>x=-329


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