Chọn thông tin đúng về bài đọc sau.

A. Calories are units of energy. They refer to the amount of energy you get from foods and drinks, and the amount of energy you use through physical activities. For example, an apple has about 80 calories, while a 1.6 km walk might use up 100 calories. Calories are important for human health, and the key is having the right amount of it.

B. Everyone needs different amounts of energy per day depending on age, size and activity levels. An athlete needs more calories than an office worker. To stay in shape, an average adult requires at least 1,800 calories per day (according to the Food and Agriculture Organization of the United Nations). If we eat just the number of calories our body needs each day, we will probably be healthy. However, eating too much can make you put on weight. To lose weight, eat fewer calories than your body burns each day.

C. These are some experts' tips to reduce calorie intake. First, you must know how many calories you need each day and always count them in your diet. Have small frequent meals and drink more water too. This will help you feel less hungry. Furthermore, avoid all sugary drinks and junk food. They are high in energy but low in nutritional value.

What happens when we eat too many calories?

A. We can put on weight

B. We will be healthy.

C. We can lose weight.

D. We can reduce calorie intake.

Phân số nào dưới đây bằng phân số  5 6 ? 

A.  15 18

B.  10 18

C.  13 18

D.  36 18

Cho hàm số f(x) có bảng biến thiên như sau

Số nghiệm của phương trình f(x^2-2)=4 là

A. 4.

B. 2.

C. 3.

D. 1.

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20 + [46 + (-210) + (-26)]

= 20 + (-190) = -170

a) /a/ = 11 => a = \(\pm\)11.

b) /a/ = -5. Không có giá trị của a.

c)/a/ = /10/ <=> /a/ = 10 => a = \(\pm\) 10

d)/-17/./a/ = -5 <=> 17./a/ = -5

<=> /a/ = \(\dfrac{-5}{17}\). Không có giá trị của a

Thực hiện các phép tính sau:

a.  2 5   +   1 4   =

b.  5 6   -   2 3   =

c. 3 4   ×   1 3 =

Đặt \(\dfrac{a}{b}=\dfrac{b}{c}=\dfrac{c}{d}=\dfrac{d}{e}=K\)

=> a = bK, b = cK, c = dK, d = eK

Do đó: \(\dfrac{2a^4+3b^4+4c^4+5d^4}{2b^4+3c^4+4d^4+5e^4}\)

= \(\dfrac{2b^4K^4+3c^4K^4+4d^4K^4+5e^4K^4}{2b^4+3c^4+4d^4+5d^4}\)

= \(\dfrac{K^4\left(2b^4+3c^4+4d^4+5d^4\right)}{2b^4+3c^4+4d^4+5d^4}\)

= K⁴ (1)

\(\dfrac{a}{e}=\dfrac{bK}{e}=\dfrac{cK^2}{e}=\dfrac{dK^3}{e}=\dfrac{eK^4}{e}=K^4\left(2\right)\)

(1)(2) => \(\dfrac{2a^4+3b^4+4c^4+5d^4}{2b^4+3c^4+4d^4+5e^4}\) = \(\dfrac{a}{e}\)

a) 9.10ⁿ + 18 = 9(10ⁿ + 2) \(⋮\) 9

Mặt khác: 9(10ⁿ + 2) = 3.3(10ⁿ + 2)\(⋮\) 3

=> 9.10ⁿ + 18 \(⋮\) 9.3

=> 9.10ⁿ + 18 \(⋮\) 27.

b) 9²ⁿ + 14 = 81ⁿ + 14.

Vì 81ⁿ có chữ số tận cùng là 1 nên 81ⁿ + 14 có chữ số tận cùng là 5.

=> 81ⁿ + 14 \(⋮\) 5

=> 9²ⁿ + 14 \(⋮\) 5