Question

[꧁ღ☠#Շђเêภ✟ภђเ✟Շử_ђàภ☠ღ꧂(#Շђáภђ✞קђá✞...]

tìm x,y biết : \(\frac{x}{3}=\frac{y}{7}\)và x.y=84

Answer 1

[╰❥ʄƖųơҳɛɬıŋɛ﹏❣ ( ๖ۣۜTεαм ๖ۣۜTαм ๖ۣ...]

đặt x/3=y/=k(k khác 0) =>x=3k;y=7k

=>x.y=3k.7k=21.k^2=84

=>k^2=4=(2)^2 hoặc(-2)^2

th1:k=2=> x=6;y=14

th2:k=-2 =>x=-6;y=-14

Answer 2

[Fire Sky]

Đặt \(\frac{x}{3}=\frac{y}{7}=k\)   ta có :

\(x=3k\) ;\(y=7k\)

Vì \(x.y=84\Rightarrow3k.7k=21k^2=84\)

\(\Rightarrow k^2=4=2^2\)

\(\Rightarrow\orbr{\begin{cases}k=-2\\k=2\end{cases}}\)

+TH1: \(k=-2\Rightarrow\hept{\begin{cases}x=-6\\y=-14\end{cases}}\)

+TH2: \(k=2\Rightarrow\hept{\begin{cases}x=6\\y=14\end{cases}}\)

Vậy (x,y) = {(-6,-14);(6,14)}