x*0,75+2.4/3.8-0.8=6.4

x*0.75+2.4/3=6.4

x*0.75+2.4/3=19.2/3

gach mau so ta co

x*0.75+2.4=19.2

x*0.75=19.2-2.4

x*0.75=16.8

x=16.8/0.75

x=22.4

k bn nha

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 ..

Thôi khỏi mình giải ra rồi

A = (-5.85)+{[+41.3)+(+5)]+9+0.85)}

A = [(-5.85+0.85)+5+41.3

A = -5+5+41.3=0+41.3=41.3

B = (-87,5)+{(+87.5)+[(+3.8)+(-0.8)]}

B =(-87.5+87.5)+3.8+(-0.8)

B = 0+3=3

C = [(+9.5)+(-13)]+[(-5)+(+8.5)

C = [(+9.5)+(-5)]+(+8.5)+(-13)

C = 4.5 + 8.5 +(-13) =13+(-13)=0

a: =0,8*5*1,25=1*5=5

b: =0,8+0,45

=1,25