Question

Bài 1:

a ) \(\dfrac{x}{5}=\dfrac{y}{7}\& x.y=140\)

b) \(\dfrac{x}{5}=\dfrac{y}{3}=\dfrac{z}{2} \& 3x-2y+7z=69\)

c) \(\dfrac{x}{5}=\dfrac{y}{4} \& x^2-y^2=1\)

d) \(5x=7y\&y-x=18\)

Giúp mk nhé :

Trần Thị Yến Nhi Phạm Hoàng Giang Nguyễn Huy Tú Ace Legona Akai Haruma

Answer 1

a)

\(\dfrac{x}{5}=\dfrac{y}{7}=k\\ \Rightarrow\left\{{}\begin{matrix}x=5k\\y=7k\end{matrix}\right.\)

\(x.y=5k.7k=35k^2=140\\ \Rightarrow k^2=4\Rightarrow k=\pm2\)

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

Answer 2

b)

\(\dfrac{x}{5}=\dfrac{y}{3}=\dfrac{z}{2}\Rightarrow\dfrac{3x}{15}=\dfrac{2y}{6}=\dfrac{7z}{14}=\dfrac{3x-2y+7z}{15-6+14}=\dfrac{69}{23}=3\)

\(\Rightarrow\left\{{}\begin{matrix}x=15\\y=9\\z=6\end{matrix}\right.\)

Answer 3

Cái j đó?

Btvn hả

Answer 4

B.3x/15=2y/6=7z/14

3x-2y+7z/15-6+14=69/23=3

...

Answer 5

c)

\(\dfrac{x}{5}=\dfrac{y}{4}\Rightarrow\dfrac{x^2}{25}=\dfrac{y^2}{16}=\dfrac{x^2-y^2}{25-16}=\dfrac{1}{9}\)

\(\Rightarrow\left\{{}\begin{matrix}x=\dfrac{5}{9}\\y=\dfrac{4}{9}\end{matrix}\right.\)

d)

\(5x=7y\Rightarrow\dfrac{x}{7}=\dfrac{y}{5}=\dfrac{y-x}{5-7}=\dfrac{18}{-2}=-9\)

\(\Rightarrow\left\{{}\begin{matrix}x=-9.7=-63\\y=-9.5=-45\end{matrix}\right.\)

Answer 6

A) dặt x/5=y/7=k(k≠0)

X/5=k;x=5.k

y/7=k;y=7.k

Có x.y=140

5.k.7.k=140

35k2=140;k2=4

K=±2

vs k=2thì:x=5.2=10;y=7.2=14

vsk=-2thì:x=5.(-2)=-10;y=7.(-2)=-14

Answer 7

Mình cảm ơn ๖ۣۜĐặng♥๖ۣۜQuý nhiều nha