\(\Leftrightarrow\dfrac{x-5}{21}=\dfrac{y-9}{35}=\dfrac{z-21}{15}=k\)

=>x-5=21k; y-9=35k; z-21=15k

=>x=21k+5; y=35k+9 z=15k+21

xyz=6720

=>(21k+5)(35k+9)(15k+21)=6720

=>\(k\simeq0,34\)

=>x=12,14; y=20,9; z=26,1

140 - 2 x ( x + 34 ) = 60

\(\Leftrightarrow2\left(x+34\right)=140-\)\(60\)

\(\Leftrightarrow2\left(x+34\right)=80\)

\(\Leftrightarrow x+34=80:2\)

\(\Leftrightarrow x+34=40\)

\(\Leftrightarrow x=40-34\)

\(\Leftrightarrow x=6\)

6 nha

kb nha

\(140-2\times\left(x+34\right)=60\)

\(\Rightarrow2\times\left(x+34\right)=140-60\)

\(\Rightarrow2\times\left(x+34\right)=80\)

\(\Rightarrow x+34=80:2\)

\(\Rightarrow x+34=40\)

\(\Rightarrow x=40-34\)

\(\Rightarrow x=6\)

Học tốt #

140-(x+60)=40

\(x+60=100\)

\(x=40\)

140-(x+60)=40

=> x+60 = 140 - 40 

=> x+60 = 100

=> x = 100 - 60

=> x = 40

Vậy x = 40 

HỌC TỐT 

(140+60) . 400 = 200.400 = 80000

140x400+60x400

=400x(140+60)

=400x200

=80000

a)

Theo tính chất của dãy tỉ số bằng nhau, ta có:

\(\dfrac{x}{5}=\dfrac{y}{25}=\dfrac{x+y}{5+25}=\dfrac{60}{30}=2\)

\(\Rightarrow\dfrac{x}{5}=2\Rightarrow x=2\times5=10\)

\(\Rightarrow\dfrac{y}{25}=2\Rightarrow y=2\times25=50\)

Vậy\(\left\{{}\begin{matrix}x=10\\y=50\end{matrix}\right.\)

b)

\(\dfrac{x}{5}=\dfrac{y}{7}\Rightarrow\left(\dfrac{x}{5}\right)^2=\left(\dfrac{y}{9}\right)^3\Rightarrow\dfrac{x}{5}\times\dfrac{x}{5}=\dfrac{x}{5}\times\dfrac{y}{7}=\dfrac{x\times y}{5\times7}=\dfrac{140}{35}=4=\left(2\right)^2\)

\(\Rightarrow\dfrac{x}{5}=2\Rightarrow x=2\times5=10\)

\(\Rightarrow\dfrac{y}{7}=2\Rightarrow y=2\times7=14\)

Vậy \(\left\{{}\begin{matrix}x=10\\y=14\end{matrix}\right.\)

x=10

A=   +  +   +     

   =   +  +   +     

   =   + 2. + 2  +     

   = 3. + 2  +

140 + 60 - ( 125 + 75 )

=200 - 200

= 0i0

K NHA Kim Ngọc Yên

140+60-(125+75)

=200-200

=0

ai k minh mih k lai

   140+60 - ( 125 + 75 )

= 200    -  200

= 0

kim ngọc yên nhớ k lại mình nha