n_Mg=x,n_Cu=y

24x +64y=20

2x + 2y =0.05*2

=>x=-0.42 => đề sai

b) 2(2x-1)+18=9(x+2)(2x+k) có nghiệm là x=1

=>2(2*1-1)+18=9(1+2)(2*1+k)

=>2+18=27(2+k)

=>2+k=20/27

=>k=-34/27

${\left(2x+1\right)}^2$(9x+2k) - 5(x+2)=40 có nghiệm là x=2

=>(2*2+1)²(9*2+2k)-5(2+2)=40

=>25(18+5k)-20=40

=>25(18+5k)=60

=>18+5k=2.4

=>5k=-15.6 =>k=-0.624

TK

Nồi cơm điện có bộ phận vỏ nồi có hai lớp và giữa hai lớp có bông thủy tinh cách nhiệt nên nhiệt độ của nồi cơm điện truyền ra bên ngoài môi trường ít giúp cho cơm mau chín. Ngược lại, dùng bếp điện thì nhiệt độ cung cấp tỏa ra bên ngoài môi trường nhiều

⇒Sử dụng nồi cơm điện tiết kiệm điện năng hơn bếp điện

P= (1 - x^2 )/ (x+1 )+(2x^2 +x)/x +x^2

P=\(\dfrac{1-x^2}{x+1}+\dfrac{x\left(2x+1\right)}{x\left(x+1\right)}\)

P=\(\dfrac{1-x^2}{x+1}+\dfrac{2x+1}{x+1}\)

P=\(\dfrac{-x^2+2x+2}{x+1}\)

TK nhé

The Vietnamese people celebrate the New Year ( Tet) on the first three days of January according to the Lunar calendar.To prepare for Tet,these days,they often paint their houses.They buy a lot of fresh fruit,flowers and make many delicious dishes.They make sticky rice cakes because they are their traditional cakes.People who work a long distance away try to get home on these days.On the first day of Tet,people often offer these good fruit and food to their ancestors and after that the whole families enjoy the food.They also visit pagodas,temples,their relatives and friends.Children are very happy to get lucky money from the adults.There are a lot of traditional games and contests at Tet such as rice-cooking, fire-making, water-fetching, buffalo-fighting, ect.They are really interesting. People are playing and enjoying themselves very much on this occasion

4/Is a poem going to be wrote by her?

1/Has the work been finished by Tom?

2/Were some exercised gave by the teacher ?

3/Has the window of the labratory been changed by them ?

Nếu bể không có nước, mở vòi chảy vào mỗi phút được 80 l thì sau : 6000/80=75(phút)