cau lam bai giai phan c nhe

A,8

B,123

C,42

:-)

thank you ban minh ngoc nhe

X x 62 - X x 52 = 420

X x ( 62 - 52 )   = 420

X x 10 = 420

       X = 420 : 10

       X = 42

X x 62 -X x52=420

X x (62-52)=420

X x10=420

=>x=42

k đúng ch0 mình nha mấy bạn

10x=420

x=42

\(\left(x-52\right)-62=52\)

\(\Rightarrow x-52=52+62\)

\(\Rightarrow x-52=114\)

\(\Rightarrow x=114+52\)

\(\Rightarrow x=166\)

\(\left(x-52\right)-62=52\)

\(x-52=52+62\)

\(x-52=114\)

\(x=114+52\)

\(x=166\)

Vậy \(x=166\)

#Ayumu

Ta có: xy=BCNN(x,y).ƯCLN(x,y)

=> 420 . ƯCLN(x,y) = 5880

=> ƯCLN(x,y) = 14

Vì (x,y) = 14 => \(\hept{\begin{cases}x=14m\\y=14n\end{cases}\left(m,n\in N;\left(m,n\right)=1\right)}\) 

Lại có: xy = 5880

=> 14m.14n = 5880

=> 196mn = 5880

=> mn = 30

Vì (m,n) = 1

Ta có bảng:

Vậy các cặp (x;y) là (14;420);(28;210);(42;140);(70;84);(84;70);(140;42);(210;28);(420;14)

Mày cũng phải làm đề amsterdam hả Hà mã

y x ( 8 + 2 ) = 420

y x 10 = 420

y = 420 : 10

y = 42

y x ( 109 - 9 ) = 2300

y x 100 = 2300

y = 23

y x 8 +y x2 = 420

yx(8+2)=420

y          =420/(8+2)

y          =420/10

y         =  42

109 x y -9 x y = 2300

y x(109-9)       =2300

y                      =2300/(109-9)

y                       =2300/100

y                       =23

thank you 

Coi x=20k, y=20h

xy=20k.20h=400.h.k =420...

\(Tacó:\)

\(xy=6.UCLN\left(x,y\right)=1\)

\(\Leftrightarrow6=xy=2.3=3.2=1.6=6.1\)

\(+xy=2.3\Rightarrow\left(x,y\right)=1\left(tm\right).Th:xy=3.2\left(tm\right)\)

\(+xy=1.6=6.1\Rightarrow\left(x,y\right)=1\left(tm\right)\)

\(\Rightarrow x,y\in\left\{\left(1;6\right),\left(6;1\right),\left(2;3\right),\left(3;2\right)\right\}\)