sai. chữa:

585 - { [ ( 156 + 93 ) : 3 ] - 3 }

= 585 - { ( 249:3 ) - 3 }

= 585 - (83-3)

= 585-80

= 505

\(1449+\left\{\left[\left(6^3+184\right):2^3\right].9^2\right\}\)

\(\Rightarrow1449+\left\{\left[\left(216+184\right):8\right].81\right\}\)

\(=1449+\left\{\left[400:8\right].81\right\}\)

\(=1449+\left\{50.81\right\}\)

\(=1449+4050=5499\)

Vậy biểu thức trên = 5499

\(585-\left\{\left[\left(156+93\right):3\right]-3\right\}\)

\(=585-\left\{\left[249:3\right]-3\right\}\)

\(=585-\left\{83-3\right\}\)

\(585-80=505\)

Vậy biểu thức trên = 505

a) ( x - 4 ) . 3 = 21

             x - 4 = 21 : 3

             x - 4 = 7

                  x = 7 + 4

                  x = 11

b) 585 - ( 7x + 60 ) = 455

                  7x + 60 = 585 - 455

                  7x + 60 = 130

                          7x = 130 - 60

                          7x = 70

                            x = 70 : 7

                            x = 10

44 + ( 16 - x ) = 50

=> 16 - x = 50 - 44

=>16 - x = 6

=> x = 16 - 6

=> x = 10

a, 14,7 x 9,5 + 24,6 - 19,24

= 139,65 + 24,6 - 19,24

= 164,25 - 19,24

= 145,01

b, 95,76 + 12,7 x 0,8 - 93

= 95,76 + 10,16 - 93

= 105,92 - 93

= 12,92

c, 156,93 - 12,4 x 8 + 17,95

= 156,93 - 99,2 + 17,95

= 57,73 + 17,95

= 75,68

\(\dfrac{x}{5}=\dfrac{y}{7}=\dfrac{z}{3}=>\left\{{}\begin{matrix}x=\dfrac{5y}{7}\\z=\dfrac{3y}{7}\end{matrix}\right.\) thay x,z vào \(x^2+y^2-z^2=585\)

\(=>\left(\dfrac{5y}{7}\right)^2+y^2-\left(\dfrac{3y}{7}\right)^2=585=>y=\pm21\)

\(=>\left\{{}\begin{matrix}x=\dfrac{5.(\pm21)}{7}=\pm15\\z=\dfrac{3\left(\pm21\right)}{7}=\pm9\end{matrix}\right.\)

vậy (x,y,z)\(\in\left\{\left(15;21;9\right)\left(-15;-21;-9\right)\right\}\)

x/5 = y/7 = z/3 =>(x/5)^2= (y/7)^2 = (z/3)^2 hay x^2/25 = y^2/49 =z^2 /9  

x^2/25 = y^2/49 =z^2 /9 = (x^2 + y^2 - z^2) /(25+49 -9)=585/65 =9=3^2  

=> (x/5)^2=3^2 =>x/5 =+-3 =>x=+-15  

(y/7)^2=3^2 =>y/7 =+-3 =>y=+-21  

(z/3)^2 =3^2 =>z/3 =+-3 =>z=+-9  

vậy có 2 cặp (x;y;z) là: (15;21;9) và (-15;-21;-9)

\(\frac{x}{5}=\frac{y}{7}=\frac{z}{3}=\frac{x^2}{25}=\frac{y^2}{49}=\frac{z^2}{9}=\frac{585}{65}=9\)

\(\Rightarrow\frac{x^2}{25}=9\Rightarrow x^2=225\Rightarrow x=15hoặc-15\)

\(\frac{y^2}{49}=9\Rightarrow y^2=441\Rightarrow y=21hoặc-21\)

\(\frac{z^2}{9}=9\Rightarrow z^2=81\Rightarrow z=9\)

\(14\times99=1386\)

\(7989-997=6992\)

\(15373-9998=5375\)

\(42\times53+47\times156-47\times114\)

\(=42\times53+47\times(156-114)\)

\(=42\times53+47\times42\)

\(=42\times(53+47)\)

\(=42\times100\)

\(=4200\)