Mk ko hiểu .....mk chả thấy gì ngoài mấy câu này.bn vít thiu à

1. Assume that \(\sqrt{2}\) is a rational number. That means there exist two integers a and b such that a / b =  \(\sqrt{2}\) 
2. So it can be written as a fractional fraction (a fraction that can not be reduced again): a / b with a, b is two primes together and (a / b)² = 2.
3. From (2) denotes a² / b² = 2 and a² = 2.b².
4. Then a² is even because it is equal to 2.b² (obviously even)
5. From this inference, a must be an even number because a² is the even number of digits (odd numbers are square rooted as odd, even square digits have square root).
6. Since a is even, there are some k satisfactions: a = 2k.
7. Substitution (6) into (3) we have: (2k)² = 2b² <=> 4k² = 2b² <=> 2k² = b².
8. Because 2k² = b² where 2k² is even, then b² is even, this inference b is also even [reason similar to (5)].
9. From (5) and (8) we have: a and b are even numbers, which contradicts the assumption that a / b is the minimal number in (2).
From the contradiction inference:  \(\sqrt{2}\)  is a rational number that is false and must conclude. \(\sqrt{2}\)  is an irrational number.

Go to this link and see the "Proofs of irrationality" : en.wikipedia.org/wiki/Square_root_of_2

Name the points and the angles as shown

Draw BP // m as shown,then BP // n since m // n.We have :

\(\widehat{B_1}=\widehat{A_1}=50^0\) (2 corresponding angles)

\(\widehat{B_2}=\widehat{C_1}=80^0\)(2 alternative interior angles)

\(\Rightarrow\widehat{ABC}=\widehat{B_1}+\widehat{B_2}=50^0+80^0=130^0\)

So,the answer is 130⁰

Let a be the number. We have :

\(\dfrac{1}{2}.\dfrac{3}{4}a-\dfrac{2}{5}a=20\Leftrightarrow\dfrac{3}{8}a-\dfrac{2}{5}a=20\Leftrightarrow\dfrac{-1}{40}a=20\Leftrightarrow a=-800\)

So, the answer is -800

We have the formula :

Volume = Length x Width x Height.

So \(120=5\cdot4\cdot height\)

So the value of the height is \(\dfrac{120}{5\cdot4}=6\left(in\right)\)

Answer : 6 in.

Giá trị của chiều cao là:

120:5:4=120:20=6 (in)

Đáp số: 6 in

The value of the height is:

120: 5 = 4 = 120: 20 = 6 (in)

Answer: 6 in

Problem: A and B have 88 marbles, B has 23 marbles. How many marbles does A have?

Solution: A has the number of marbles is: 88 - 23 = 65 ( marbles)

Answer: 65 marbles 

Vấn đề:Một cái hộp có 88 viên bi,trong đó số viên bi đen là 23.Tính tỉ số phần trăm số bi còn lại so với số bi trong hộp.

Giải:

  số bi còn lại là

       88-23=65 viên

  tỉ số phần trăm giữa số bi còn lại và số bi trong hộp là

         65:88x100=73,86%

                    đ/s:73,86%

The numbers which are written as the sum of two prime numbers are:

4 = 2 + 2

5 = 2 + 3

6 = 3 + 3

7 = 2 + 5

8 = 3 + 5

9 = 7 + 2

10 = 5 + 5

12 = 7 + 5

13 = 11 + 2

14 = 7 + 7

15 = 13 + 2

16 = 13 + 3

18 = 11 + 7

19 = 17 + 2

So the numbers left are: 1, 2, 3, 11, 17

The sum of all positive integers less than 20 that cannot be written as the sum of two prime numbers is:

1 + 2 + 3 + 11 + 17 = 34