\(\frac{x-40}{9}=\frac{72-x}{7}\)

=> 7 ( x - 40 ) = 9 ( 72 - x )

     7 x - 280   = 648 - 9 x

     7 x + 9 x   = 648 + 280

       16 x        = 928

            x        = 58

\(\frac{x-40}{9}=\frac{72-x}{7}\)

\(\Rightarrow\left(x-40\right).7=9.\left(72-x\right)\)

\(\Rightarrow648-9x=7x-280\)

\(\Rightarrow\left(-280\right)-648=\left(-9x\right)-7x\)

\(\Rightarrow-928=-16x\)

\(\Rightarrow x=58\)

Tính giá trị biểu thức:

d) D=\(\frac{3x-2y}{x-3y}\)với \(\frac{x}{y}=\frac{10}{3}\)

\(\text{Cách 1:}\)

    \(\frac{72-x}{7}=\frac{x-40}{9}\)

=> \(\left(72-x\right)\cdot9=\left(x-40\right)\cdot7\)

=> \(648-9x=7x-280\)

=> \(648+280=7x+9x\)

=> \(16x=928\)=> \(x=928:16=58\)

\(\text{Cách 2:}\)

\(\text{Áp dụng tính chất dãy tỉ số bằng nhau, ta có:}\)

\(\frac{72-x}{7}=\frac{x-40}{9}=\frac{72-x+x-40}{7+9}=\frac{32}{16}=2\)

\(\text{Ta suy ra:}\)

\(\frac{72-x}{7}=2\)=> \(72-x=2\cdot7=14\)=> \(x=72-14=58\)

\(\text{Vậy }x=58\)

a) \(\frac{x}{6}^2=\frac{24}{25}\)

\(\Rightarrow x^2.25=6.24\)

\(\Rightarrow x^2.25=144\)

\(\Rightarrow x^2=144\div25\)

\(\Rightarrow x^2=5,76=2,4^2=\left(-2,4^2\right)\)

\(\Rightarrow x\in\left\{2,4;-2,4\right\}\)

Vậy \(x\in\left\{2,4;-2,4\right\}\)

b) \(\frac{72-x}{7}=\frac{x-40}{9}\)

\(\Rightarrow\left(72-x\right).9=\left(x-40\right).7\)

\(\Rightarrow648-9x=7x-280\)

\(\Rightarrow\left(-280\right)-648\) \(=-9x-7x\)

\(\Rightarrow-928=-16x\)

\(\Rightarrow x=58\)

Vậy \(x=58\)

=> (72 - x) . 9 = (x - 40) . 7

=> 648 - 9x = 7x - 280

=> (-280) - 648 = -9x - 7x

-928 = -16x

=> x = 58

a.

\(\frac{x}{4}=\frac{3}{2}\)

\(x=\frac{3}{2}\times4\)

\(x=6\)

b.

\(\frac{x}{16}=\frac{9}{x}\)

\(x\times x=16\times9\)

\(x^2=144\)

\(x^2=\left(\pm12\right)^2\)

\(x=\pm12\)

Vậy \(x=12\) hoặc \(x=-12\)

c.

\(\frac{x^2}{6}=\frac{24}{25}\)

\(x^2=\frac{24}{25}\times6\)

\(x^2=\frac{144}{25}\)

\(x^2=\left(\pm\frac{12}{5}\right)^2\)

\(x=\pm\frac{12}{5}\)

Vậy \(x=\frac{12}{5}\) hoặc \(x=-\frac{12}{5}\)

d.

\(\frac{72-9}{7}=\frac{x-40}{9}\)

\(\frac{x-40}{9}=\frac{63}{7}\)

\(x-40=\frac{63}{7}\times9\)

\(x-40=81\)

\(x=81+40\)

\(x=121\)

1.

b) \(\frac{72-x}{7}=\frac{x-40}{9}\)

\(\Rightarrow\left(72-x\right).9=\left(x-40\right).7\)

\(\Rightarrow648-9x=7x-280\)

\(\Rightarrow648+280=7x+9x\)

\(\Rightarrow928=16x\)

\(\Rightarrow x=928:16\)

\(\Rightarrow x=58\)

Vậy \(x=58.\)

Chúc bạn học tốt!

a) (72-x).9=7.(x-40)

   648-9x=7x-280

648+280=7x+9x (chuyển vế)

928=16x

x=928:16=58

b) (37-x).7=3.(x+13)

 259-7x=3x+39

259-39=3x+7x

220=10x

x=220:10=22

c)(x-1).(x+3)=(x-2).(x+2)

x²+3x-x-3=x²+2x-2x-4

(x²-x²)+(3x-x-2x+2x)=-4+3

0+2x=-1

x=-1/2

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Bạn tham khảo nhé! Mình đã làm ở đây rồi

a./ \(\frac{x}{5}=\frac{y}{7}=\frac{z}{4}=\frac{x-y+z}{5-7+4}=\frac{-10}{2}=-5\)

\(\Rightarrow x=-25;y=-35;z=-20\)

b./ \(\frac{x}{5}=\frac{y}{-4}=\frac{z}{-7}=\frac{x+y-z}{5-4-\left(-7\right)}=\frac{-40}{6}=-5\)

\(\Rightarrow x=-25;y=20;z=35\)