= 249 x 17 - 249 x 111 - 51 x 111 + 17 x 51

 = 17 x (249+51) - 111.(249+51)

 = 17 x 300 - 111 x 300

 = 300 x (17-111)

 = 300 x (-94)

 = -28200

Tk mk nha

\(\dfrac{33}{38}:\dfrac{11}{19}=\dfrac{33\times19}{38\times11}=\dfrac{3\times1}{2\times1}=\dfrac{3}{2}\)

3phần2

1) x : 7 + 20 = 17 x 49 + 17 x 51

x : 7 +20 = 17 x ( 49+51)

x : 7 +20 =1700

x : 7 = 1700 - 20 =1680

x = 1680 x 7 =11 760

2) 287 - ( x+ 34) x 3 - 25 = 142

287-(x+34)x3 = 142 + 25 =167

( x+34) x 3 = 287 - 167=120

x + 34 = ``120 : 3 =40

x = 40 - 34 = 6

3)13x + 15x + 12x = 120

40x = 120

x = 120 : 40 = 3

17⋮x; 21⋮x và 51⋮x \(\Rightarrow\) x \(\in\) ƯC(17,21,51)

Vì 17 là SNtố \(\Rightarrow\) ƯCLN(17,21,51) = 1 

\(\Rightarrow\) x \(\in\) Ư(1) = {1; -1}

Giải:

\(\left[{}\begin{matrix}17⋮x\\21⋮x\\51⋮x\end{matrix}\right.\) \(\Rightarrow x\inƯC\left(17;21;51\right)\) 

\(17=17\) 

\(21=3.7\) 

\(51=3.17\) 

\(\RightarrowƯCLN\left(17;21;51\right)=1\)  

\(\RightarrowƯC\left(17;21;51\right)=Ư\left(1\right)=\left\{\pm1\right\}\) 

\(\Rightarrow x\in\left\{\pm1\right\}\)

bực mình

40851

\(\dfrac{39}{17}\cdot\dfrac{51}{52}=\dfrac{3}{4}\cdot3=\dfrac{9}{4}\)

`1989/884`

`39/17 xx 51/52`

`= (39 xx 51)/(17 xx 52)`

`= 2,25`

a(17/4x12/7-2/7x17/4-3/7x17/4)x6/51

=[17/4x(12/7-2/7-3/7)]x6/51

=17/4x1x6/51

=17/4x6/51

=102/204=1/2

b,45x16-17/45x15+28

=15x3x16-17/45x15+28

=15x48-17/45x15+28

=15x2160/45-17/45x15+28

=15x(2160/45-17/45)+28

=15x2143/45+28

=2143/3+84/3

=2227/3

tính nhanh à,lên google search í

  (Người THÀNH CÔNG luôn có một lối đi riêng)

49439808/11

\(=\dfrac{36\cdot22\cdot51}{11\cdot17\cdot72}=\dfrac{1}{2}\cdot3\cdot2=3\)

-51 -17 +x =0

x =51+17

x =68