Bài 4:

a: xy=-2

=>\(x\cdot y=1\cdot\left(-2\right)=\left(-2\right)\cdot1=\left(-1\right)\cdot2=2\cdot\left(-1\right)\)

=>\(\left(x,y\right)\in\left\{\left(1;-2\right);\left(-2;1\right);\left(-1;2\right);\left(2;-1\right)\right\}\)

b: \(\left(x-1\right)\left(y+2\right)=-3\)

=>\(\left(x-1\right)\cdot\left(y+2\right)=1\cdot\left(-3\right)=\left(-3\right)\cdot1=-1\cdot3=3\cdot\left(-1\right)\)

=>\(\left(x-1;y+2\right)\in\left\{\left(1;-3\right);\left(-3;1\right);\left(-1;3\right);\left(3;-1\right)\right\}\)

=>\(\left(x,y\right)\in\left\{\left(2;-5\right);\left(-2;-1\right);\left(0;1\right);\left(4;-3\right)\right\}\)

Bài 3:

a: \(x\left(x+9\right)=0\)

=>\(\left[{}\begin{matrix}x=0\\x+9=0\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=0\\x=-9\end{matrix}\right.\)

b: \(\left(x-5\right)^2=9\)

=>\(\left[{}\begin{matrix}x-5=3\\x-5=-3\end{matrix}\right.\)

=>\(\left[{}\begin{matrix}x=3+5=8\\x=-3+5=2\end{matrix}\right.\)

c: \(\left(7-x\right)^2=-64\)

mà \(\left(7-x\right)^2>=0\forall x\)

nên \(x\in\varnothing\)

Bài 2:

a: \(\left(-31\right)\cdot x=-93\)

=>\(31\cdot x=93\)

=>\(x=\dfrac{93}{31}=3\)

b: \(\left(-4\right)\cdot x=-20\)

=>\(4\cdot x=20\)

=>\(x=\dfrac{20}{4}=5\)

c: \(5x+1=-4\)

=>\(5x=-4-1=-5\)

=>\(x=-\dfrac{5}{5}=-1\)

d: \(-12x+1=-4\)

=>\(-12x=-4-1=-5\)

=>\(12x=5\)

=>\(x=\dfrac{5}{12}\)

đậu xanh trả lời nhanh nhận 1 đống quà

 a) 27 x 39 + 27 x 63 - 2 x 2

= 27 x ( 39 + 63 ) - 2 x 2

= 27 x 102 - 2 x 2

= 2754 - 4

= 2750

b) 48 x 19 + 48 x 115 + 134 x 52

= 48 x ( 19 +115 ) + 134 x 52

= 48 x 134 + 134 x 52

= ( 48 + 52 ) x 134

= 100 x 134

= 13400

chúc các bạn năm mới vui vẻ. bạn tk mk nha.

a) 27 x 39 + 27 x 63 - 2 x 2

= 27 x (39 + 63) - 2 x 2

= 27 x 102 - 2 x 2

= 2754 - 4

= 2750

b) 48 x 19 + 48 x 115 + 134 x 52

= 48 x (19 + 115) + 134 x 52

= 48 x 134 + 134 x 52

= 134 x (48 + 52)

= 134 x 100

= 13400

a,27.39+27.63-2.2

=27.(39+63)-4

=27.102-4

=2754-4

=2750

b,48.19+48.115+134.52

=48.(19+115)+134.52

=48.134+134.52

=134.(48+52)

=134.100

=13400

sorry toán lớp 6

b.124 : 0,25 + 6 x 124 

=124 : 25/100 + 6 x 124

= 124 x 100/25 + 6 x 124

=124 x 4 + 6 x124

= 124 x(4 + 6)

= 124 x10

=1240

c,2 x 5,5 + 24,6 x 1,5

=11 + 36,9 

=47,9

d,3/4 x 24,8 + 12,4 x 8,5

=18,6 + 12,4 x 8,5

=18,6 + 105,4

=124

Chúc bạn học tốt!

Bài 1 : Tìm x

96-x.(x+1)=42

x(x+1)=138

2x+x=138

3x=138

x=46

Bài 2 : Tính Nhanh

a,19.27+47.81+19.20

=19.(27+20)+47.81

=19.47+47.81

=47(19+81)

=47.100

=4700

b,87.23+13.93+70.87

=87.(23+70)+13.93

=87.93+13.93

=93.(87+13)

=93.100

=9300

Bài 3: Tính Tổng

a,1+4+7+...+79

=(79+1).27:2

=80.27:2

=2160:2

=1080

b,15+17+19+21+...+151+153+155

=(155+15).71:2

=160.71:2

=11360:2

=5680

c,15+25+35+...+115

=130.11:2

=1430:2

=715

d,24+25+28+...+125+126

=150.103:2

=7725

Đề có đúng không bạn?

a) 1 267 + 99 + 501 = 1 267 + (99 + 501)

                                = 1 267 + 600 = 1 867

     25 x 14 x 4 = (25 x 4) x 14

                       = 100 x 14 = 1 400

b) 3 905 x (50 – 1) = 3 905 x 50 – 3 905 x 1

                             = 195 250 – 3 905 = 191 345

     270 : ( 27 x 2 ) = 270 : 27 : 2

                             = 10 : 2 = 5

c) 115 x 58 + 115 x 42 = 115 x (58 + 42)

                                   = 115 x 100 = 11 500

136 x 67 – 136 x 66 = 136 x (67 – 66)

                              = 136 x 1 = 136