\(\dfrac{x}{3}=\dfrac{y}{7};x.y=84\)
Đặt \(\dfrac{x}{3}=\dfrac{y}{7}=k\)
⇒ x = 3k ; y = 7k
⇒ x . y = 3k . 7k
⇒ 84 = 21 . k2
⇒ k2 = \(\dfrac{84}{21}=4\)
⇒ k = \(\pm2\)
+ ) Nếu k = 2 ⇒ \(\left\{{}\begin{matrix}x=2.3=6\\y=2.7=14\end{matrix}\right.\)
+ ) Nếu k = -2 ⇒ \(\left\{{}\begin{matrix}x=-2.3=-6\\y=-2.7=-14\end{matrix}\right.\)
Vậy ( x , y ) ∈ { ( 6 , 14 ) ; (-6 , -14 ) }
CHÚC BẠN HỌC TỐT
Tìm x
a) 2.(4 x - 30 ) -3 (x + 5) + 4( x - 10 ) = 5 (x + 2)
b) \(\dfrac{11}{12}\)- ( \(\dfrac{2}{5}\) + x ) = \(\dfrac{2}{3}\) . ( 6 x + 1)
c) \(\dfrac{7}{3}\)- ( 2 x - \(\dfrac{1}{3}\) ) = ( \(-2\dfrac{1}{6}\) + \(1\dfrac{1}{2}\) ) : 0,25
d) 0,75 + \(\dfrac{5}{9}\) : x = \(5\dfrac{1}{2}\)
\(\dfrac{x}{y}=\dfrac{17}{3}vàx+y=-60\)
Tìm x biết
a) 7 - \(\sqrt{x}\) = 0 d) 4x2 -1 =0
b)5\(\sqrt{x}\) + 1 = 40 e) \(\sqrt{x+1}\) - 2 = 0
c)\(\dfrac{5}{12}\)\(\sqrt{x}\) - \(\dfrac{1}{6}\) = \(\dfrac{1}{3}\) f) 2x2 + 0,82 = 1
g) ( 2\(\dfrac{1}{3}\) + 3\(\dfrac{1}{2}\)) : ( x + 3\(\dfrac{1}{7}\)) + 7\(\dfrac{1}{2}\)
GIÚP MK NHA MK ĐAG CẦN GẤP CHIỀU NỘP RỒI
Tìm x,y biết:
\(\dfrac{3x-y}{x+y}\) =\(\dfrac{3}{4}\) và x-y=4
1)Tính tỉ số \(\dfrac{A}{B}=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{2007}+\dfrac{1}{2008}+\dfrac{1}{2009}}{\dfrac{2008}{1}+\dfrac{2007}{2}+\dfrac{2006}{3}+...+\dfrac{2}{2007}+\dfrac{1}{2008}}\)
2) chứng minh: \(\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}+\dfrac{7}{3^2.4^2}+..+\dfrac{19}{9^2.10^2}< 1\)
Tìm x
\(\left|3,5-x\right|+\dfrac{2}{7}=\dfrac{16}{7}\)
Tính :
\(M=\left(2\dfrac{1}{3}+3,5\right):\left(-4\dfrac{1}{6}+3\dfrac{1}{7}\right)+7,5\)
Tìm n nhỏ nhất để các phân số sau đây tối giản
\(\dfrac{1}{n+3};\dfrac{2}{n+4};\dfrac{3}{n+5};.........;\dfrac{2015}{n+2017};\dfrac{2016}{n+2018}\)
Thực hiện các phép tính :
a) \(\left(\dfrac{9}{25}-2,18\right):\left(3\dfrac{4}{5}+0,2\right)\)
b) \(\dfrac{5}{18}-1,456:\dfrac{7}{25}+4,5.\dfrac{4}{5}\)
