1. Find the quadratic equation 2x + 3Y = - 20 2, find the quadratic equation 4x + y = 16

1. Find the quadratic equation 2x + 3Y = - 20 2, find the quadratic equation 4x + y = 16

Hello!
There are innumerable solutions to a quadratic equation of two variables

Using image method to solve equations x + y = 5,2x + y = 8

First, in the same coordinate system, make a straight line y = - x + 5 (just take any two points, such as x = 0 to get y = 5; take x = 5 to get y = 0. Connect points (0,5) and (5,0) to get a straight line y = - X.) and a straight line y = - 2x + 8 (the same as the first one). Then make a vertical line to the X and Y axes through the intersection of the two lines. The perpendicular coordinates on the X and Y axes are the X and Y solutions of the given equations, that is, x = 3, y = 2

To solve the equations: 2x − 3Y = 85y − 7x = 5

(1) X 7 + (2) × 2 is - 11y = 66, y = - 6. Substituting y = - 6 into (1) is: 2x + 18 = 8, x = - 5. The solution of the original equations is x = − 5Y = − 6

M-N: Mn = N-M: 1 times 4 / 3 + 3 times 4 / 5 +19 times 4 / 21
It's urgent

4/1*3 +4/3*5+...+4/19*21∵（m-n）/mn=1/n - 1/m∴1/mn=[1/(m-n）]（1/n -1/m）∴1/1*3=[1/（3-1）]（1/1-1/3）=(1/2)（1/1-1/3）∴1/3*5=[1/（5-3）]（1/3-1/5）=(1/2)（1/3-1/5）∴1/5*7=[1/（7-5）]（1/5-1/7）=...

It takes 7 hours for a freight car to drive from city a to city B, and 132 kilometers per hour for a bus to drive from city B to city A. if two cars leave from city a and city B at the same time and meet each other in three and one-third of an hour, how many kilometers are there between city a and city B?

3 and 1 / 3 hours, that is, 10 / 3 hours, then (10 / 3) / 7 = 10 / 21,
Then the bus takes 1-10 / 21 of the whole journey = 11 / 21
132 * 10 / 3 = 440km
440km, accounting for 11 / 21 of the whole journey
Whole course = 440 / (11 / 21) = 840km

1×2×3×4×…… ×499×500=

1×2×3×4×…… ×499×500=500!
It's the factorial of 500

Energy conversion in spaceship flight (Physics)
(1) How does the kinetic energy, gravitational potential energy and mechanical energy change when the spacecraft moves from the far point to the near point in the elliptical orbit around the earth?
(2) How does the mechanical energy and internal energy change when the spacecraft returns to the earth through the atmosphere, opens a huge parachute at high altitude, and falls at a constant speed near the ground/
(3) One side of the "Shenzhou five good" return capsule on display in the Beijing ship sky museum is black. Try to explain why it is black! Is the black side facing the ground or facing away from the ground?

(1) From the apogee to the perigee, the kinetic energy increases because the velocity increases gradually. According to the conservation of energy, the kinetic energy increases and the corresponding gravitational potential energy decreases. Because there is no energy loss, the total amount of mechanical energy remains unchanged

The equation is formulated according to the following conditions: 5 times of a number is 10 times larger than the number; the difference between 5 times of a number and 9 is half of the number; a number is 2 times smaller than 7 times
Three times the sum of a number and four is five times greater than this number

Let this number be X
(1) Five times a number is ten times greater than that number
　　5x-x=10
　　x=2.5
(2) The difference between five times a number and nine is half that number
　　5x-9=x/2
　　10x-x=18
　　x=2
(3) A certain number is two times smaller than seven
　　7x-x=2
　　x=1/3
(4) Three times the sum of a number and four is five times greater than this number
　　(x+4)×3=x+5
　　2x=-7
　　x=-7/2

Is the friction force related to the contact area?

Don't mislead me, the friction force F = ν FN, where ν is the friction coefficient and FN is the pressure
So it doesn't matter

If a and B are fixed values, the solution of the equation (2kA + x) / 3 - (x-bx) / b = 2 is always 1 no matter what the value of K is. Find the value of a and B

（2 ka+x）/3-(x-bx)/b=2
2ka/3+x/3-x/b+x=2
No matter what the value of K is, its solution is always 1
2ka/3=0
a=0
X / 3-x / B + x = 2, the solution is always 1
1/3-1/b+1=2
b=-3/2