=\(\dfrac{135}{2}\) hay 67.5

135/2

67.5

a) 7.28=x.x

=> 196=x²

=> \(\left(\pm14\right)^2=x^2\)

=> x=\(\pm14\)

b) DK: x≠-17

pt<=> 4.(10+2)=6.(17+x)

=> 4.12=17.6+6x

=> 48-102=6x

=>-66=6x

=>x=-11

c) 7.(x+40)=6.(17+x)

=> 7x+280=102+6x

=> 7x-6x=102-280

=> x=-178

Giải:

a) \(\dfrac{7}{x}=\dfrac{x}{28}\)

\(\Leftrightarrow x^2=196\)

\(\Leftrightarrow x=\pm\sqrt{196}=\pm14\)

Vậy ...

b) \(\dfrac{10+2}{17+x}=\dfrac{3}{4}\)

\(\Leftrightarrow40+8=51+3x\)

\(\Leftrightarrow3x=40+8-51=-3\)

\(\Leftrightarrow x=-\dfrac{3}{3}=-1\)

Vậy ...

c) \(\dfrac{40+x}{17+x}=\dfrac{6}{7}\)

\(\Leftrightarrow280+7x=102+6x\)

\(\Leftrightarrow7x-6x=102-280\)

\(\Leftrightarrow x=-178\)

Vậy ...

B1:

a,7 . 28 = x . x => 196 = x^2 => x = 14

Tớ chỉ bít làm bài 1a ko làm đc các bài còn lại!!!

ai bit lam lam ho minh vs di ak pls

lau thessssss

Ta có \(x1-\frac{1}{9}=x2-\frac{2}{8}=...=x9-\frac{9}{1}\)

\(=\frac{x1-1}{9}=\frac{x2-2}{8}=\frac{x3-3}{7}=...=\frac{x9-9}{1}\)

= \(\frac{x1-1+x2-2+x3-3+...+x9-9}{9+8+7+...+1}\)

\(=\frac{\left(x1+x2+x3+...+x9\right)-\left(1+2+3+...+9\right)}{9+8+7+....+1}\)

=\(\frac{90-45}{45}=\frac{45}{45}=1\)

=> \(\hept{\begin{cases}\begin{cases}x1=10\\x2=10\end{cases}\\.....\\x9=10\end{cases}}\)

\(=2^2\cdot3=12\)

\(\dfrac{2^7\times9^2}{3^3\times2^5}=\dfrac{2^7\times3^4}{3^3\times2^5}=2^2\times3=4\times3=12\)