Làm sao 2 ẩn mà chỉ có 1 phương trình mà giải đc nhỉ ??

Thầy cho bọn tớ thế !

Ta có : \(\frac{6}{8}=\frac{3}{4}\)

\(\frac{x}{y}=\frac{3}{4}\)

\(\Rightarrow4x=3y\)

\(\Rightarrow x=3;y=4\)

A = 1/2^2 + 1/3^2 + 1/4^2 + ... + 1/100^2

1/2^2 < 1/1*2

1/3^2 < 1/2*3

1/4^2 < 1/3*4

...

1/100^2 < 1/99*100

=> A < 1/1*2 + 1/2*3 + 1/3*4 + ... + 1/99*100

=> A < 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/99 - 1/100

=> A < 1 - 1/100

=> A < 1

minh deo can ban k dau :((

\(a,\frac{1}{2}x+\frac{3}{5}(x-2)=3\)

\(\Rightarrow\frac{1}{2}x+\frac{3}{5}x-\frac{6}{5}=3\)

\(\Rightarrow\left[\frac{1}{2}+\frac{3}{5}\right]x=3+\frac{6}{5}\)

\(\Rightarrow\left[\frac{5}{10}+\frac{6}{10}\right]x=\frac{21}{5}\)

\(\Rightarrow\frac{11}{10}x=\frac{21}{5}\)

\(\Rightarrow x=\frac{21}{5}:\frac{11}{10}=\frac{21}{5}\cdot\frac{10}{11}=\frac{21}{1}\cdot\frac{2}{11}=\frac{42}{11}\)

Vậy x = 42/11

còn đây là câu b

\(\frac{3x-2-30}{6}=\frac{3-2x-14}{4}\)

\(\Leftrightarrow\frac{3x-32}{6}-\frac{-11-2x}{4}=0\)

\(\Leftrightarrow\frac{6x-64+33+6x}{12}\)

\(\Leftrightarrow12x=31\)

\(\Leftrightarrow x=\frac{31}{12}\)

\(\frac{10x-10+4-21x+3}{12}=\frac{4x+3-35}{7}\)

\(\Leftrightarrow\frac{-11x-3}{12}=\frac{4x-3}{7}\)

\(\Leftrightarrow\frac{-11x-3}{12}-\frac{4x-3}{7}=0\)

\(\frac{-77x-21-48x+36}{84}=0\)

\(\Leftrightarrow125x=15\)

\(\Leftrightarrow x=\frac{3}{25}\)

thanks nha

 o0oNguyễno0o bn giúp mk nha bài này khó wa

 Harry Potter05 giúp mk đc ko vậy bn!!!

 o0oNguyễno0o giúp mk nhanh ik nha

\(\frac{4}{3}.\left(\frac{1}{6}-\frac{1}{2}\right)\le x\le\frac{2}{3}.\left(\frac{-1}{6}+\frac{3}{4}\right)\)

\(\frac{4}{3}.\frac{-1}{3}\le x\le\frac{2}{3}.\frac{7}{12}\)

\(\frac{-4}{9}\le x\le\frac{7}{18}\)

\(\frac{-8}{18}\le x\le\frac{7}{18}\)

\(\Rightarrow\)X \(\in\) {\(\frac{-7}{18};\frac{-6}{18};\frac{-5}{18};\frac{-4}{18};\frac{-3}{18};\frac{-2}{18};\frac{-1}{18};0;\frac{1}{18};\frac{2}{18};\frac{3}{18};\frac{4}{18};\frac{5}{18};\frac{6}{18}\)}

\(\left(\frac{5}{x+3}-2\right).4=7-\left(\frac{9}{x+3}+\frac{1}{2}\right).2\)

\(\Leftrightarrow\frac{20}{x+3}-8=7-\frac{18}{x+3}+1\)

\(\Leftrightarrow\frac{20}{x+3}-8=8-\frac{18}{x+3}\)

\(\Leftrightarrow\frac{20}{x+3}+\frac{18}{x+3}=8+8\)

\(\Leftrightarrow\frac{38}{x+3}=16\)

\(\Leftrightarrow x+3=2,375\)

\(\Leftrightarrow x=-0,625\)

\(\left(\frac{5}{x+3}-2\right).4=7-\left(\frac{9}{x+3}+\frac{1}{2}\right).2\)

\(\Leftrightarrow\frac{20}{x+3}-8=7-\left(\frac{18}{x+3}+1\right)\)

\(\Leftrightarrow\frac{20}{x+3}-8=7-\frac{18}{x+3}-1\)

\(\Leftrightarrow\frac{20}{x+3}+\frac{18}{x+3}=7-1+8\)

\(\Leftrightarrow\frac{38}{x+3}=14\)

\(\Leftrightarrow\left(x+3\right)14=38\)

\(\Leftrightarrow14x+42=38\)

\(\Leftrightarrow14x=-4\Leftrightarrow x=-\frac{4}{14}=-\frac{2}{7}\)

Vậy \(x=-\frac{2}{7}\)

TRẻ Trâu 

\(\frac{x+6}{15}=\frac{5-x}{7}\)

\(\Leftrightarrow\left(x+6\right).7=\left(5-x\right).15\)

\(\Leftrightarrow7x+42=75-15x\)

\(\Leftrightarrow7x+15x=75-42\)

\(\Leftrightarrow22x=33\)

\(\Leftrightarrow x=\frac{3}{2}\)

=> 7.(x+6)= 15.(5-x)

=> 7x +7.6=15.5-15x

=> 7x + 42= 75 -15x

=> 7x+15x=75-42

=> 22x=33

=>x= 1,5

\(\frac{x+6}{15}=\frac{5-x}{7}\)

\(\Rightarrow\frac{x+6}{15}-\frac{5-x}{7}=0\)

\(\Rightarrow\frac{7.\left(x+6\right)}{7.15}+\frac{15.\left(x-5\right)}{7.15}=0\)

\(\Rightarrow\frac{7x+42}{105}+\frac{15x-75}{105}=0\)

\(\Rightarrow\frac{7x+42+15x-75}{105}=0\)

\(\Rightarrow\frac{22x-33}{105}=0\)

\(\Rightarrow22x+33=0\Rightarrow22x=33\)

\(\Rightarrow x=\frac{33}{22}=\frac{3}{2}\)