a: \(\Leftrightarrow2x=\dfrac{19}{5}:\dfrac{3}{32}=\dfrac{608}{15}\)

hay x=304/15

b: \(\Leftrightarrow0.25x=20\)

hay x=80

c: \(\Leftrightarrow x=\dfrac{1}{100}:\dfrac{5}{2}=\dfrac{2}{500}=\dfrac{1}{250}\)

d: \(\Leftrightarrow0.1x=\dfrac{2}{3}:\dfrac{5}{3}=\dfrac{2}{5}\)

hay \(x=\dfrac{2}{5}:\dfrac{1}{10}=\dfrac{20}{5}=4\)

Bài 1 :

Áp dụng t.c tỉ lệ thức là làm dc thôi bn

Bài 2 :

Đặt :

\(\dfrac{x}{4}=\dfrac{y}{7}=k\)\(\Leftrightarrow\left\{{}\begin{matrix}x=4k\\y=7k\end{matrix}\right.\)\(\left(1\right)\)

Thay \(xy=112\) vào \(\left(1\right)\) ta có :

\(4k.7k=112\)

\(\Leftrightarrow28k^2=112\)

\(\Leftrightarrow k^2=4\)

\(\Leftrightarrow\left[{}\begin{matrix}k^2=2^2\\k^2=\left(-2\right)^2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}k=2\\k=-2\end{matrix}\right.\)

+) \(k=2\)\(\Leftrightarrow\left\{{}\begin{matrix}x=4.2=8\\y=7.2=14\end{matrix}\right.\)

+) \(k=-2\)\(\Leftrightarrow\left\{{}\begin{matrix}x=4.\left(-2\right)=-8\\y=7.\left(-2\right)=-14\end{matrix}\right.\)

Vậy ..

a)  \(X=\frac{2}{-7}\)và \(Y=\frac{-3}{11}\)

Ta có: \(\frac{2}{-7}>\frac{-3}{7}>\frac{-3}{11}\)

\(\Rightarrow\frac{-2}{7}>\frac{-3}{11}\Rightarrow x>y\)

b) + c) \(X=-0,75\)và\(Y=\frac{-3}{4}\)

Ta có: \(-0,75=\frac{-3}{4}=\frac{-3}{4}\)

\(\Rightarrow x=y\)

a: \(-12:\left(\frac34-\frac56\right)^2\)

\(=-12:\left(\frac{9}{12}-\frac{10}{12}\right)^2\)

\(=-12:\left(-\frac{1}{12}\right)^2=-12\cdot144=-1728\)

b: \(10\cdot\sqrt{0,01}\cdot\sqrt{\frac{16}{9}}+3\sqrt{49}-\frac16\cdot\sqrt4\)

\(=10\cdot0,1\cdot\frac43+3\cdot7-\frac16\cdot2\)

\(=\frac43+21-\frac13=21+1=22\)

c: Đặt \(\frac{x}{6}=\frac{y}{3}=\frac{z}{2}=k\)

=>x=6k; y=3k; z=2k

x-2y+4z=8

=>\(6k-2\cdot3k+4\cdot2k=8\)

=>8k=8

=>k=1

=>\(\begin{cases}x=6\cdot1=6\\ y=3\cdot1=3\\ z=2\cdot1=2\end{cases}\)

d: \(\left|\frac14+x\right|-\frac13=\frac25\)

=>\(\left|x+\frac14\right|=\frac25+\frac13=\frac{11}{15}\)

=>\(\left[\begin{array}{l}x+\frac14=\frac{11}{15}\\ x+\frac14=-\frac{11}{15}\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac{11}{15}-\frac14=\frac{44-15}{60}=\frac{29}{60}\\ x=-\frac{11}{15}-\frac14=\frac{-44-15}{60}=-\frac{59}{60}\end{array}\right.\)

\(2\dfrac{3}{4}:x=3\dfrac{1}{7}:0,01\)

\(\dfrac{11}{4}:x=\dfrac{22}{7}:\dfrac{1}{100}\)

\(\dfrac{11}{4}:x=\dfrac{2200}{7}\)

\(x=\dfrac{11}{4}:\dfrac{2200}{7}\)

\(x=\dfrac{7}{800}\)

a) \(0,25\left(x+\frac{1}{2}\right)+\frac{3}{4}+x=\frac{1}{2}\)

\(\Leftrightarrow0,25x+\frac{1}{8}+\frac{3}{4}+x=\frac{1}{2}\)

\(\Leftrightarrow1,25x=-\frac{3}{8}\)

\(\Leftrightarrow x=-\frac{3}{10}\)

c) \(2x^2+4x=0\)

\(\Leftrightarrow2x\left(x+2\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x+2=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x=-2\end{array}\right.\)

a) 0,25(x+1/2) + 3/4 + x= 1/2

<=> \(0,25x+\frac{1}{8}+\frac{3}{4}+x=\frac{1}{2}\)

<=> \(\frac{5}{4}x=\frac{1}{2}-\frac{1}{8}-\frac{3}{4}=-\frac{3}{8}\)

<=> x=\(-\frac{3}{10}\)

B) 1/2 ÷(x+7/5)-1/5=0.75

<=> \(\frac{1}{2}:\left(x+\frac{7}{5}\right)-\frac{1}{5}=\frac{3}{4}\)

<=> \(\frac{1}{2x}+\frac{5}{14}-\frac{1}{5}=\frac{3}{4}\)

<=> \(\frac{1}{2x}=\frac{3}{4}+\frac{1}{5}-\frac{5}{14}=\frac{83}{140}\)

<=> x=\(\frac{70}{83}\)

C) 2x^2 + 4x= 0

\(x\left(x+2\right)=0\)

<=> x=0 hoặc x=-2

D) x^2 + 4x = 0<=> x(x+4)=0

<=> x=0 hoặc x=-4

a)

Vì -22 < -21 và 77> 0 nên x <y

b)

Vì -216 < -213 và 300 > 0 nên y < x

c)

Vậy x=y