Bạn thử xem lại đề nhé, giữa 3 số này là dấu cộng hay dấu nhân.

Nếu là dấu cộng thì ta có:

Nếu là dấu nhân thì ta có:

\(\text{1.-(-66)+34+(-73)-27+99}.\)

\(=66+34-73-27+99=100-100+99=-99.\)

\(\text{2.54-(45-30+54)-30+5}.\)

\(54-45+30-54-30+5=\left(54-54\right)+\left(-45+5\right)+\left(30-30\right)=-40.\)

\(\text{3.42-56+33-(33-56+42)}.\)

\(=42-56+33-33+56-42=\left(42-42\right)+\left(-56+56\right)+\left(33-33\right)=0.\)

\(\text{4.50-(47+50-18)+(47-18)}.\)

\(=50-47-50+18+47-18=\left(50-50\right)+\left(-47+47\right)+\left(18-18\right)=0.\)

\(\text{5.10-(28-30+4)}.\)

\(=10-28+30-4=10+30-20-8-4=20-12=8.\)

\(\text{6.-(-73)+(44-94+27)+94}.\)

\(=73+44-94+27+94=\left(73+27\right)+\left(-94+94\right)+44=100+44=144.\)

1: =66+34-73-27+99=99

2: =54-45+30-54-30+5=-40

3: =42-56+33-33+56-42=0

4: =50-47-50+18+47-18=0

5: =10-28+30-4=2-4+10=12-4=8

1; - (-66) + 34 + (-73) - 27 + 99 

=  66 + 34 - 73 - 27 + 99

=  (66 + 34) - (73 + 27) + 99

=  100 - 100 + 99

=  0 + 99

=    99

2; 54 - (45 - 30 + 54) - 30 + 5

= 54 - 45 + 30 - 54 - 30 + 5

= (54 - 54) + (30 - 30) - (45 - 5)

= 0 + 0 - 40

= - 40 

3; 42 - 56 + 33 - (33 + 56 + 42)

= 42 - 56 + 33 - 33 - 56 - 42

= (42 - 42) - (33 - 33) - (56 + 56)

= 0 - 0 - 112

= - 112 

a) \(5x\left(x-7\right)-30\cdot\left(x-7\right)=0\)

   \(\Rightarrow\left(5x-30\right)\left(x-7\right)=0\)

   \(\Rightarrow\left[{}\begin{matrix}5x-30=0\\x-7=0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=6\\x=7\end{matrix}\right.\)

b) \(\left(2x-4\right)\left(2x+4\right)-x\left(x+3\right)=3x\left(x+5\right)\)

   \(\Rightarrow4x^2-16-x^2-3x=3x^2+15x\)

   \(\Rightarrow-16=18x\Rightarrow x=-\dfrac{8}{9}\)

x= 5³:5

x=5²

25

x=25

a, Ta có: 10 = 2.5; 12 =  2 2 .3

BCNN(10,12) = 2 2 .3.5 = 60

b, Ta có: 24 =  2 3 .3; 56 =  2 3 .7

BCNN(24;56) =  2 3 .3.7 = 168

c, Ta có: 84 =  2 2 .3.7; 108 =  2 2 . 3 3

BCNN(84;108) =  2 2 . 3 3 .7

d, Ta có: 33 = 3.11; 44 = 4.11; 55 = 5.11

BCNN(33;44;55) = 3.4.5.11 = 660

e, Ta có: 8 =  2 3 ; 18 = 2. 3 2 ; 30 = 2.3.5

BCNN(8,18,30) =  2 3 . 3 2 . 5 = 360

f, Ta có: 40 =  2 3 . 5 ; 28 =  2 2 .7; 140 =  2 2 .5.7

BCNN(40;28;140) =  2 3 . 5 . 7 = 280

\(\frac{1}{3}-\left(\frac{1}{3.4}-\frac{1}{4.5}-...-\frac{1}{7.8}\right)=x-\frac{5}{18}\)

\(x-\frac{5}{18}=\frac{1}{3}-\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{7}-\frac{1}{8}\right)\)

\(x-\frac{5}{18}=\frac{1}{3}-\frac{1}{3}+\frac{1}{8}\)

\(x-\frac{5}{18}=0+\frac{1}{8}\)

\(x-\frac{5}{18}=\frac{1}{8}\)

\(x=\frac{1}{8}+\frac{5}{18}\)

\(x=\frac{9}{72}+\frac{20}{72}\)

\(x=\frac{29}{72}\)

1/3 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56 = x - 5/18

            1/4 - 1/20 - 1/30 - 1/42 - 1/56 = x - 5/18

                        1/5 - 1/30 - 1/42 - 1/56 = x - 5/18

                                    1/6 - 1/42 - 1/56 = x - 5/18

                                                1/7 - 1/56 = x - 5/18

                                                            1/8 = x - 5/18

                                                                x=1/8+5/18

                                                                x= 29/72

                                                           Vậy : x = 29/72