a) Ta có: 2^91 = (2^13)^7 = 8192^7

5^35 = (5^5)^7 = 3125^7

Vì 8192 > 3125 nên 8192^7 > 3125^7

Vậy 2^91 > 5^35

b) Ta có: 9999^10 = 99^10 . 101^10

Vì 99^2 < 99^10 nên 99^2 < 99^10 . 101^10

Vậy 99^2 < 9999^10

c) Ta có: 2^300 = (2^6)^50 = 64^50

3^200 = (3^4)^50 = 81^50

Vì 49 < 64 < 81 nên 49^50 < 64^50 < 81^50

Vậy 49^50 < 2^300 < 3^200

d) 9^3/25^3 = (9/25)^3

3^6/2^12 = (3^2)^3/(2^4)^3 = 9^3/16^3 = (9/16)^3

Vì 9/25 < 9/16 nên (9/25)^3 < (9/16)^3

Vậy 9^3/25^3 < 3^6/2^12.

Ta có: a/b = 10/9 => a/10 = b/9 

b/c = 3/4 => b/3 = c/4 => b/9 = c/12

=> a/10 = b/9 = c/12

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

 a/10 = b/9 = c/12 = a - b + c / 10 - 9 + 12 = 78/13 = 6

a/10 = 6 => a = 6 . 10 = 60

b/9 = 6 => b = 6 . 9 = 54

c/12 = 6 => c = 6 . 12 = 72

Vậy a = 60; b = 54 và c = 72.

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

  \(\frac{12a-15b}{7}\)  = \(\frac{20c-12a}{9}\)  = \(\frac{15b-20c}{11}\) = \(\frac{12a-15b+20c-12a+15b-20b}{7+9+11}\) = \(\frac{0}{27}\) = 0

=> a = b = c

Mà a + b + c = 48

=> a = b = c = 48 : 3 = 16

Vậy a = b = c = 16.

x-7=19:19

x-7=1

x=1+7

x=8

Ta có:x=\(\frac{a}{m}\)<=>x=\(\frac{2a}{2m}\)

         y=\(\frac{b}{m}=>y=\frac{2b}{2m}\)

         z=\(\frac{\left(a+b\right)}{2m}\)

mà x<y  nên a<b (với m>0)

=>a+a<a+b<b+b

hay 2a<a+b<2b

1. The students in class 7C enjoy different activities after school hours.

2. At present Nga is taking an English course on Monday, Wednesday and Friday afternoons.

3. Han practises playing the music with some other students or twice a week.

4. .......... Peter, Mary has a beautiful collection of stamps.(câu này mik ko biết)

5. In my free time, i sometimes listen to music. Sometimes i lie on the couch in front of the TV.

6. My grandfether still likes to take part in social activies.

7. Are you tired to watching advertisements on TV ?

8. There are few TV programs for teenagers.

318 + ( 96 - x ) = 414

           96 - x   = 414 - 318

           96 - x   = 96

                  x  = 96 - 96

                  x  = 0

**** ! ^ - ^

Cảm ơn bạn nhiều nha!! ^_^ 

Tính giá trị biểu thức biết.....??????

Biết gì vậy bạn???????

Bạn ghi thiếu đề kìa!

5 Lan: You shouldn't eat so much in the evening.

3 Lan: Oh, dear. How long have you had that?

6 Minh: I know. What should I do now?

1 Lan: You don't look very well. Are you OK?

2 Minh: No. I have stomachache. 

9 Lan: So take some medicine and go to bed.

8 Minh: I don't like going to the doctor.

10 Minh: Good idea.

4 Minh: It started last night. I ate a big Chinese meal.

7 Lan: You should go to the doctor.