Phần c khó để tớ giải cho

a) Tìm $x$

$\dfrac{3}{(x+2)(x+5)}+\dfrac{5}{(x+5)(x+10)}+\dfrac{7}{(x+10)(x+17)}=\dfrac{x}{(x+2)(x+17)}$

ĐKXĐ: $x\ne-2;\,-5;\,-10;\,-17$.

Ta có:

$\dfrac{3}{(x+2)(x+5)}=\dfrac{1}{x+2}-\dfrac{1}{x+5}$

$\dfrac{5}{(x+5)(x+10)}=\dfrac{1}{x+5}-\dfrac{1}{x+10}$

$\dfrac{7}{(x+10)(x+17)}=\dfrac{1}{x+10}-\dfrac{1}{x+17}$

Suy ra: $\dfrac{1}{x+2}-\dfrac{1}{x+17}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow\dfrac{15}{(x+2)(x+17)}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow x=15$.

Vậy: $x=15$.

câu a;b: bạn áp dụng công thức \(\frac{a}{n.\left(n+a\right)}=\frac{1}{n+a}-\frac{1}{n}\left(a\inℕ^∗\right)\)

a)

Điều kiện: $x\ne-2,-5,-10,-17.$

$\dfrac3{(x+2)(x+5)}+\dfrac5{(x+5)(x+10)}+\dfrac7{(x+10)(x+17)}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow\dfrac1{x+2}-\dfrac1{x+5}+\dfrac1{x+5}-\dfrac1{x+10}+\dfrac1{x+10}-\dfrac1{x+17}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow\dfrac1{x+2}-\dfrac1{x+17}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow\dfrac{15}{(x+2)(x+17)}=\dfrac{x}{(x+2)(x+17)}$

$\Leftrightarrow x=15.$

b)

Điều kiện: $x\ne1,3,8,20.$

$\dfrac2{(x-1)(x-3)}+\dfrac5{(x-3)(x-8)}+\dfrac{12}{(x-8)(x-20)}-\dfrac1{x-20}=-\dfrac34$

$\Leftrightarrow\left(\dfrac1{x-3}-\dfrac1{x-1}\right)+\left(\dfrac1{x-8}-\dfrac1{x-3}\right)+\left(\dfrac1{x-20}-\dfrac1{x-8}\right)-\dfrac1{x-20}=-\dfrac34$

$\Leftrightarrow-\dfrac1{x-1}=-\dfrac34$

$\Leftrightarrow\dfrac1{x-1}=\dfrac34$

$\Leftrightarrow4=3(x-1)$

$\Leftrightarrow3x=7$

$\Leftrightarrow x=\dfrac73.$

c) \(\frac{x-1}{2009}+\frac{x-2}{2008}=\frac{x-3}{2007}+\frac{x-4}{2006}\)

\(\Leftrightarrow\left(\frac{x-1}{2009}-1\right)+\left(\frac{x-2}{2008}-1\right)=\left(\frac{x-3}{2007}-1\right)+\left(\frac{x-4}{2006}-1\right)\)

\(\Leftrightarrow\frac{x-2010}{2009}+\frac{x-2010}{2008}-\frac{x-2010}{2007}-\frac{x-2010}{2006}=0\)

\(\Leftrightarrow\left(x-2010\right).\left(\frac{1}{2009}+\frac{1}{2008}-\frac{1}{2007}-\frac{1}{2006}\right)=0\)

\(\Leftrightarrow x-2010=0\)

\(\Leftrightarrow x=0+2010\)

\(\Rightarrow x=2010\)

Vậy \(x=2010.\)

Mình chỉ làm câu c) thôi nhé.

Chúc bạn học tốt!

Vì các phân số đều có dạng  
 
 
 

=>phần này dễ rùi bn tự lm nhé tích trung tỉ ngoại tỉ

a)\(\frac{x+1}{5}+\frac{x+3}{4}=\frac{x+5}{3}+\frac{x+7}{2}\)

\(\Leftrightarrow\frac{12\left(x+1\right)}{60}+\frac{15\left(x+3\right)}{60}=\frac{20\left(x+5\right)}{60}+\frac{30\left(x+7\right)}{60}\)

\(\Leftrightarrow12x+12+15x+45=20x+100+30x+210\)

\(\Leftrightarrow27x+57=50x+310\)

\(\Leftrightarrow27x+57-50x-310=0\)

\(\Leftrightarrow-23x-253=0\)

\(\Leftrightarrow x=-\frac{253}{23}\)

b)Tự làm 

Thank you nha!!!

\(\left(x-\frac{2}{5}\right).\frac{3}{4}+1=\frac{17}{20}\)

\(\left(x-\frac{2}{5}\right).\frac{3}{4}=\frac{17}{20}-1\)

\(x-\frac{2}{5}=\frac{-3}{20}:\frac{3}{4}\)

\(x=\frac{-1}{5}+\frac{2}{5}=\frac{1}{5}\)

\(\sqrt{x}=9\)=>x=81.

a)  \(\Leftrightarrow\frac{x+7}{2003}+1+\frac{x+4}{2006}+1-\frac{x-1}{2011}-1-\frac{x-5}{2015}-1=0\)

     \(\Leftrightarrow\frac{x+2010}{2003}+\frac{x+2010}{2006}-\frac{x+2010}{2011}-\frac{x+2010}{2015}=0\)

     \(\Leftrightarrow\left(x+2010\right)\left(\frac{1}{2003}+\frac{1}{2006}-\frac{1}{2011}-\frac{1}{2015}\right)=0\)

     \(\Leftrightarrow x+2010=0\) ( vì 1/2003  +  1/2006  --  1/2011  -- 1/2015   \(\ne\)0)

    \(\Leftrightarrow x=-2010\)

câu b làm tương tự (có gì không hiểu hỏi mk nha) >v<