3: \(\left|x-\dfrac{3}{4}\right|-\dfrac{1}{2}=0\)

\(\Leftrightarrow\left|x-\dfrac{3}{4}\right|=\dfrac{1}{2}\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{3}{4}=\dfrac{1}{2}\\x-\dfrac{3}{4}=-\dfrac{1}{2}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{4}\\x=\dfrac{1}{4}\end{matrix}\right.\)

c: Ta có: \(\dfrac{1}{3}-\dfrac{7}{8}x=\dfrac{1}{4}\)

\(\Leftrightarrow x\cdot\dfrac{7}{8}=\dfrac{1}{12}\)

\(\Leftrightarrow x=\dfrac{1}{12}\cdot\dfrac{8}{7}=\dfrac{2}{21}\)

d: Ta có: \(\dfrac{3}{2}x+\dfrac{1}{7}=\dfrac{7}{8}\cdot\dfrac{64}{49}\)

\(\Leftrightarrow x\cdot\dfrac{3}{2}=1\)

hay \(x=\dfrac{2}{3}\)

mình lười nên nói cách làm nhé

B1: chuyển \(\dfrac{6}{x^2-9}\)sang vế trái và thêm dấu trừ ở trc \(\dfrac{6}{x^2-9}\)và vế phải =0

B2: để ý thấy \(x^2-9\)=(x-3).(x+3) tức là hằng đẳng thức số 3 ý

B3: quy đồng mẫu , mẫu số chung là (x-3).(x+3).(2x+7)

B4: chia cả hai vế cho (x-3).(x+3).(2x+7)

lưu ý : bước này là dấu⇒ chứ ko phải dấu ⇔ nhé

B5: giải pt như bình thg thui

ĐKXĐ: \(x\notin\left\{3;-3;-\dfrac{7}{2}\right\}\)

Ta có: \(\dfrac{13}{\left(x-3\right)\left(2x+7\right)}+\dfrac{1}{2x+7}=\dfrac{6}{x^2-9}\)

\(\Leftrightarrow\dfrac{13\left(x+3\right)}{\left(x-3\right)\left(x+3\right)\left(2x+7\right)}+\dfrac{x^2-9}{\left(2x+7\right)\left(x-3\right)\left(x+3\right)}=\dfrac{6\left(2x+7\right)}{\left(x-3\right)\left(x+3\right)\left(2x+7\right)}\)

Suy ra: \(13x+39+x^2-9=12x+42\)

\(\Leftrightarrow x^2+13x+30-12x-42=0\)

\(\Leftrightarrow x^2+x-12=0\)

\(\Leftrightarrow x^2+4x-3x-12=0\)

\(\Leftrightarrow x\left(x+4\right)-3\left(x+4\right)=0\)

\(\Leftrightarrow\left(x+4\right)\left(x-3\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+4=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-4\left(nhận\right)\\x=3\left(loại\right)\end{matrix}\right.\)

Vậy: S={-4}

a: =>4x-6-9=5-3x-3

=>4x-15=-3x+2

=>7x=17

hay x=17/7

b: \(\Leftrightarrow\dfrac{2}{3x}-\dfrac{1}{4}=\dfrac{4}{5}-\dfrac{7}{x}+2\)

=>2/3x+21/3x=4/5+2+1/4=61/20

=>23/3x=61/20

=>3x=23:61/20=460/61

hay x=460/183

a) \(\dfrac{3x-1}{x-1}-\dfrac{2x+5}{x+3}=1-\dfrac{4}{\left(x-1\right)\left(x+3\right)}\)

ĐKXĐ \(x-1\ne0\) hoặc \(x+3\ne0\)

\(\Rightarrow x\ne1\) và \(x\ne-3\)

\(\dfrac{\left(3x-1\right)\left(x+3\right)}{\left(x-1\right)\left(x+3\right)}-\dfrac{\left(2x+5\right)\left(x-1\right)}{\left(x-1\right)\left(x+3\right)}=\dfrac{\left(x-1\right)\left(x+3\right)}{\left(x-1\right)\left(x+3\right)}-\dfrac{4}{\left(x-1\right)\left(x+3\right)}\)

\(\Leftrightarrow\left(3x-1\right)\left(x+3\right)-\left(2x+5\right)\left(x-1\right)=\left(x-1\right)\left(x+3\right)-4\)

\(\Leftrightarrow3x^2+9x-x-3-\left(2x^2-2x+5x-5\right)=x^2+3x-x-3-4\)

\(\Leftrightarrow3x^2+9x-x-3-2x^2+2x-5x+5=x^2+3x-x-3-4\)

\(\Leftrightarrow9x-x+2x-5x-3x+x=3-5-3-4\)

\(\Leftrightarrow3x=-9\)

\(\Leftrightarrow x=-3\) (không thỏa ĐK)

Vậy PTVN

b) \(\dfrac{13}{\left(x-3\right)\left(2x+7\right)}+\dfrac{1}{2x+7}=\dfrac{6}{\left(x-3\right)\left(x+3\right)}\)

ĐKXĐ: \(x-3\ne0\Rightarrow x\ne3\)

\(x+3\ne0\Rightarrow x\ne-3\)

\(2x+7\ne0\Rightarrow2x\ne-7\Rightarrow x\ne\dfrac{-7}{2}\)

\(\dfrac{13\left(x+3\right)}{\left(x-3\right)\left(x+3\right)\left(2x+7\right)}+\dfrac{\left(x-3\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)\left(2x+7\right)}=\dfrac{6\left(2x+7\right)}{\left(x-3\right)\left(x+3\right)\left(2x+7\right)}\)

\(\Leftrightarrow13\left(x+3\right)+\left(x-3\right)\left(x+3\right)=6\left(2x+7\right)\)

\(\Leftrightarrow13x+39+x^2+3x-3x-9=12x+42\)

\(\Leftrightarrow x^2+x-12=0\)

\(\Leftrightarrow x^2-3x+4x-12=0\)

\(\Leftrightarrow x\left(x-3\right)+4\left(x-3\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x+4\right)=0\)

\(\left\{{}\begin{matrix}x-3=0\\x+4=0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=3\left(KTĐK\right)\\x=-4\left(TĐK\right)\end{matrix}\right.\)

Vậy S={-4}

a) \(\dfrac{3x-1}{x-1}-\dfrac{2x+5}{x+3}=1-\dfrac{4}{\left(x-1\right)\left(x+3\right)}\) ( đk: x ≠ 1 ; x ≠ -3 )

\(\Leftrightarrow\left(3x-1\right)\left(x+3\right)-\left(2x+5\right)\left(x-1\right)=\left(x-1\right)\left(x+3\right)-4\)

\(\Leftrightarrow3x^2+9x-x-3-2x^2+2x-5x+5=x^2+3x-x-3-4\)

\(\Leftrightarrow3x=-9\)

\(\Rightarrow x=-3\left(KTM\right)\)

S = ∅

b) \(\dfrac{13}{\left(x-3\right)\left(2x+7\right)}+\dfrac{1}{2x+7}=\dfrac{6}{\left(x-3\right)\left(x+3\right)}\)

( đk: x ≠ ± 3 ; x ≠ \(\dfrac{-7}{2}\) )

\(\Leftrightarrow13\left(x+3\right)+\left(x-3\right)\left(x+3\right)=6\left(2x+7\right)\)

\(\Leftrightarrow13x+39+x^2-9=12x+42\)

\(\Leftrightarrow x^2-x-12=0\)

\(\Leftrightarrow x^2+3x-4x-12=0\)

\(\Leftrightarrow x\left(x+3\right)-4\left(x+3\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(x+3\right)=0\)

\(\Rightarrow\left\{{}\begin{matrix}x-4=0\\x-3=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=4\left(TM\right)\\x=3\left(KTM\right)\end{matrix}\right.\)

S = \(\left\{4\right\}\)

Tính hợp lí: 

a) \(\left(-0,4\right)+\dfrac{3}{8}+\left(-0,6\right)\)

\(=\left[\left(-0,4\right)+\left(-0,6\right)\right]+\dfrac{3}{8}\)

\(=-1+\dfrac{3}{8}\)

\(=\dfrac{\left(-8\right)+3}{8}\)

\(=\dfrac{-5}{8}\)

b) \(\dfrac{4}{5}-1,8+0,375+\dfrac{5}{8}\)

\(=\dfrac{4}{5}-\dfrac{9}{5}+\dfrac{3}{8}+\dfrac{5}{8}\)

\(=-1+1\)

\(=0\\\)

c) \(\dfrac{7}{3}.\left(-2,5\right).\dfrac{6}{7}\)

\(=\dfrac{7}{3}.\dfrac{-5}{2}.\dfrac{6}{7}\)

\(=\dfrac{7}{3}.\dfrac{6}{7}.\dfrac{-5}{2}\)

\(=2.\dfrac{-5}{2}\)

\(=-5\)

d) \(\dfrac{7}{12}.\left(-2,34\right)-\dfrac{7}{12}.\left(-0,34\right)\)

\(=\dfrac{7}{12}.\left[\left(-2,34\right)+0,34\right]\)

\(=\dfrac{7}{12}.\left(-2\right)\)

\(=\dfrac{-7}{6}\)

e) \(\dfrac{-8}{3}.\dfrac{2}{11}-\dfrac{8}{3}:\dfrac{11}{9}\)

\(=\dfrac{8}{3}.\dfrac{-2}{11}-\dfrac{8}{3}.\dfrac{9}{11}\)

\(=\dfrac{8}{3}.\left(\dfrac{-2}{11}-\dfrac{9}{11}\right)\)

\(=\dfrac{8}{3}.-1\)

\(=\dfrac{-8}{3}\)

Chúc bạn học tốt

Cảm ơn nha.

a)\(\left(-0,4\right)+\dfrac{3}{8}+\left(-0,6\right)=\left(-\dfrac{4}{10}\right)+\dfrac{3}{8}+\left(-\dfrac{6}{10}\right)=-\dfrac{2}{5}+\dfrac{3}{8}-\dfrac{3}{5}=-\dfrac{2}{5}-\dfrac{3}{5}+\dfrac{3}{8}=-1+\dfrac{3}{8}=-\dfrac{5}{8}\)

b) \(\dfrac{4}{5}-1,8+0,375+\dfrac{5}{8}=\dfrac{4}{5}+\dfrac{5}{8}-1,425=\dfrac{57}{40}-\dfrac{1425}{1000}=\dfrac{57}{40}-\dfrac{57}{40}=0\)

c) \(\dfrac{7}{3}.\left(-2,5\right).\dfrac{6}{7}=\dfrac{7}{3}.\dfrac{6}{7}.\left(-\dfrac{25}{10}\right)=-5\)

d) \(\dfrac{7}{12}.\left(-2,34\right)-\dfrac{7}{12}.\left(-0,34\right)=\dfrac{7}{12}.\left(-2,34-0,34\right)=\dfrac{7}{12}.\left(-2,68\right)=\dfrac{7}{12}.\left(-\dfrac{268}{100}\right)=-\dfrac{7}{12}.\dfrac{4}{25}=-\dfrac{7}{75}\)

e) \(\dfrac{-8}{3}.\dfrac{2}{11}-\dfrac{8}{3}:\dfrac{11}{9}=-\dfrac{8}{3}.\left(\dfrac{2}{11}+\dfrac{9}{11}\right)=-\dfrac{8}{3}.1=-\dfrac{8}{3}\)

a: \(\Leftrightarrow\dfrac{5}{2}:\left|\dfrac{3}{4}x+\dfrac{1}{2}\right|=\dfrac{15}{4}-3=\dfrac{3}{4}\)

\(\Leftrightarrow\left|\dfrac{3}{4}x+\dfrac{1}{2}\right|=\dfrac{5}{2}:\dfrac{3}{4}=\dfrac{5}{2}\cdot\dfrac{4}{3}=\dfrac{20}{6}=\dfrac{10}{3}\)

=>3/4x+1/2=10/3 hoặc 3/4x+1/2=-10/3

=>3/4x=17/6 hoặc 3/4x=-23/6

=>x=34/9 hoặc x=-46/9

b: \(\Leftrightarrow\dfrac{9}{4}:\left|x+\dfrac{1}{3}\right|=6.5-2=\dfrac{9}{2}\)

\(\Leftrightarrow\left|x+\dfrac{1}{3}\right|=\dfrac{9}{4}:\dfrac{9}{2}=\dfrac{1}{2}\)

=>x+1/3=1/2 hoặc x+1/3=-1/2

=>x=1/6 hoặc x=-5/6

\(\left\{{}\begin{matrix}\dfrac{7}{\sqrt{x}-7}-\dfrac{4}{\sqrt{y}+6}=\dfrac{5}{3}.\\\dfrac{5}{\sqrt{x}-7}+\dfrac{3}{\sqrt{y}+6}=2\dfrac{1}{6}.\end{matrix}\right.\) \(\left(x,y\ge0;x\ne49\right).\)

\(\Leftrightarrow\left\{{}\begin{matrix}7\dfrac{1}{\sqrt{x}-7}-4\dfrac{1}{\sqrt{y}+6}=\dfrac{5}{3}.\\5\dfrac{1}{\sqrt{x}-7}+3\dfrac{1}{\sqrt{y}+6}=\dfrac{13}{6}.\end{matrix}\right.\)

Đặt \(\dfrac{1}{\sqrt[]{x}-7}=a\); \(\dfrac{1}{\sqrt[]{y}+6}=b\left(a,b\ne0\right).\)

\(\Rightarrow\left\{{}\begin{matrix}7a-4b=\dfrac{5}{3}.\\5a+3b=\dfrac{13}{6}.\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{1}{3}.\\b=\dfrac{1}{6}.\end{matrix}\right.\) \(\left(TM\right).\)

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{1}{\sqrt{x}-7}=\dfrac{1}{3}.\\\dfrac{1}{\sqrt{y}+6}=\dfrac{1}{6}.\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}\sqrt{x}-7=3.\\\sqrt{y}+6=6.\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}\sqrt{x}=10.\\\sqrt{y}=0.\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=100\left(TM\right).\\y=0\left(TM\right).\end{matrix}\right.\)

Vậy hệ phương trình có nghiệm duy nhất là: \(\left(x;y\right)=\left(100;0\right).\)

a) Ta có: \(\dfrac{x+4}{5}-x+4=\dfrac{x}{3}-\dfrac{x-2}{2}\)

\(\Leftrightarrow\dfrac{6\left(x+4\right)}{30}-\dfrac{30x}{30}+\dfrac{120}{30}=\dfrac{10x}{30}-\dfrac{15\left(x-2\right)}{30}\)

\(\Leftrightarrow6x+24-30x+120=10x-15x+30\)

\(\Leftrightarrow-24x+144=-5x+30\)

\(\Leftrightarrow-24x+5x=30-144\)

\(\Leftrightarrow-19x=-114\)

hay x=6

Vậy: S={6}

b) Ta có: \(\dfrac{4-5x}{6}=\dfrac{2\left(-x+1\right)}{2}\)

\(\Leftrightarrow2\cdot\left(4-5x\right)=12\left(-x+1\right)\)

\(\Leftrightarrow2-10x=-12x+12\)

\(\Leftrightarrow2-10x+12x-12=0\)

\(\Leftrightarrow2x-10=0\)

\(\Leftrightarrow2x=10\)

hay x=5

Vậy: S={5}

c) Ta có: \(\dfrac{-\left(x-3\right)}{2}-2=\dfrac{5\left(x+2\right)}{4}\)

\(\Leftrightarrow\dfrac{2\left(3-x\right)}{4}-\dfrac{8}{4}=\dfrac{5\left(x+2\right)}{4}\)

\(\Leftrightarrow6-2x-8=5x+10\)

\(\Leftrightarrow-2x+2-5x-10=0\)

\(\Leftrightarrow-7x-8=0\)

\(\Leftrightarrow-7x=8\)

hay \(x=-\dfrac{8}{7}\)

Vậy: \(S=\left\{-\dfrac{8}{7}\right\}\)

d) Ta có: \(\dfrac{7-3x}{2}-\dfrac{5+x}{5}=1\)

\(\Leftrightarrow\dfrac{5\left(7-3x\right)}{10}-\dfrac{2\left(x+5\right)}{10}=\dfrac{10}{10}\)

\(\Leftrightarrow35-15x-2x-10-10=0\)

\(\Leftrightarrow-17x+15=0\)

\(\Leftrightarrow-17x=-15\)

hay \(x=\dfrac{15}{17}\)

Vậy: \(S=\left\{\dfrac{15}{17}\right\}\)

a) Ta có: ⇔6(x+4)30−30x30+12030=10x30−15(x−2)30⇔6(x+4)30−30x30+12030=10x30−15(x−2)30

hay x=6

Vậy: S={6}

b) Ta có: 

Vậy: 7−3x2−5+x5=17−3x2−5+x5=1

Vậy: x+45−x+4=x3−x−22x+45−x+4=x3−x−22

hay x=5

Vậy: S={5}

c) Ta có: ⇔2(3−x)4−84=5(x+2)4⇔2(3−x)4−84=5(x+2)4

hay S={−87}S={−87}

d) Ta có: ⇔5(7−3x)10−2(x+5)10=1010⇔5(7−3x)10−2(x+5)10=1010

hay S={1517}