Write 21 as the sum of two prime numbers

Write 21 as the sum of two prime numbers

21=2+19

The sum of two prime numbers is 21. What are the two prime numbers (prime numbers) respectively
Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry! Hurry!

2 and 19

Can you fill in the right prime on the line? 15=______ +______ 8=______ +______ 34=______ +______ 20=______ +______ ．

15 = 2 + 138 = 3 + 534 = 5 + 2920 = 3 + 17

The mixed operation of 1-2 / 1 + 3 / 1 =? Rational number

1-2 / 1 + 3 / 1
=1/2+1/3
=5/6
That's five out of six

If sin θ and cos θ are the two roots of the equation x & # 178; - MX + M = 0, find the value of Tan θ + (1 / 2 of Tan θ)

According to the relationship between root and coefficient, it is concluded that: 1
sinθ+cosθ=m
sinθcosθ=m
Because: (sin θ + cos θ) & # 178; = Sin & # 178; θ + cos & # 178; θ + 2Sin θ cos θ
That is: M & # 178; - 2m-1 = 0, the solution is: M = 1 ± √ 2
tanθ+1/tanθ
=sinθ/cosθ+cosθ/sinθ
=(sin²θ+cos²θ)/sinθcosθ
=1/m
When m = 1 + √ 2, Tan θ + 1 / Tan θ = 1 / (1 + √ 2) = √ 2-1
When m = 1 - √ 2, Tan θ + 1 / Tan θ = 1 / (1 - √ 2) = - √ 2-1

What's the car logo of a circle and an a in the middle?

It should be the sign of Chery
Do you think it's such a sign?

A strict definition of the symmetry of a line in a function image?
F (x + m) = f (M-X) how to prove the symmetry of "function image" with respect to straight line?
I think it's the definition of symmetry

Prove: take any point P (a, b) in the function image
Then B = f (a)
Because f (a) = f (A-M + m) = f [M - (A-M)] = f (2m-A)
So B = f (2m-A)
So the point Q (2m-A, b) is also on the graph of function y = f (x)
It is easy to know that P (a, b) and Q (2m-A, b) are symmetric with respect to the line x = M
So the point P (a, b) symmetric with respect to the line x = m is on the image of the function y = f (x)
Note the arbitrariness of point P
So the image of the function y = f (x) is symmetric with respect to the line x = M

The school organized spring outings. 52 students went boating in the park. They rented a total of 11 boats. Each boat took 6 people and each boat took 4 people. How many boats did they rent?

If there are x large ships, then there are 11-x small ships
formulation of equation
6x+4(11-x)=52
x=4
Boat 11-4 = 7

Let p be a point on the ellipse x ^ 2 + y ^ 2 = 1, and F1 and F2 be the two focuses of the ellipse, then the absolute value of Pf1 multiplied by the maximum and minimum absolute value of PF2 is

That's a good question
1. X & # 178; + Y & # 178; = 1 is the equation of a circle. Although a circle is a special ellipse, it is generally not done in high school
&So I guess the equation of ellipse in the question is X & # 178 / A & # 178; + Y & # 178 / B & # 178; = 1
2. | Pf1 | and | PF2 | are not the absolute values of Pf1 and PF2, but the modules of vector Pf1 and vector PF2
 
Let | PF2 | = m, a-c ≤ m ≤ a + C
From the first definition of ellipse, | Pf1 | + | PF2 | = 2A
∴|PF1|=2a-|PF2|=2a-m
∴|PF1|×|PF2|=(2a-m)m
∵ A & # 178; - C & # 178; ≤ (2a-m) m ≤ A & # 178; that is, B & # 178; ≤ (2a-m) m ≤ A & # 178;
The minimum value of | Pf1 | x | PF2 | is B & # 178, and the maximum value is a & # 178;

A car travels 80km per hour from place a to place B, and a truck travels 75KM per hour from place B to place A. six hours later, the two cars meet. How many km is the distance between place a and place B?
I don't think it's necessary to solve the equation. If you want to solve the equation, how to solve it

No need
Let's set the total length to X
Then there is: X - (70 + 80) * 6 = 0, x = 150 * 6 = 900