If 4 / (x ^ 2-1) = A / (x + 1) + B / (x-1) is an identity, then why is a =? B =? A + B equal to 0

If 4 / (x ^ 2-1) = A / (x + 1) + B / (x-1) is an identity, then why is a =? B =? A + B equal to 0

answer:
Right = A / (x + 1) + B / (x-1)
=[A(x-1)+B(x+1)]/[(x+1)(x-1)]
=[Ax+Bx+B-A]/(x^2-1)
=[(A+B)x+B-A]/(x^2-1)
Because the left side = 4 / (x ^ 2-1) and the equation holds, if the denominator is the same, then the molecules should be the same
So (a + b) x + B-A = 4
If this formula holds for any x, then a + B = 0, B-A = 4
If you solve the equation, you get a = - 2, B = 2
A + B = 0 is obtained by comparing the coefficients on both sides of the identity (a + b) x + B-A = 4

Let a = {x ″ x ″ be greater than or equal to - 1 and less than or equal to 2} B = {x ″ x ″ be greater than or equal to 0 and less than or equal to 4} then what is a ∩ B?

{x/0≤x≤2}

The relationship among density, mass and volume
Density should be equal to mass divided by volume
But why isn't density inversely proportional to mass; directly proportional to volume?
It has nothing to do with mass or volume
Please help me answer this question!

Because that is only a rough formula, which refers to the relationship between the three under the same conditions, namely constant temperature and constant pressure
The mass is invariable (low speed is relative to the speed of light) and the volume of an object changes with temperature and pressure
So it can't be said that density is inversely proportional to mass; it's directly proportional to volume

Given A-B = 4, ab = 3, find 1 / 4 times (a + b) square
A quarter is a quarter
(a + b) 2 which 2 is the square

(a+b)^2=a^2+b^2+2ab=a^2+b^2-2ab+4ab=(a-b)^2+4ab=16+12=28
1/4*(a+b)^2=1/4*28=7

The standard equation of parabola with vertex at origin and focus f (0, - 2)

The standard equation of parabola with vertex at origin and focus f (0, - 2)
x^2=-8y

A working cycle of a gasoline engine consists of four strokes, which reduces the temperature of the cylinder block. There is a water tank outside the cylinder, so that the cylinder is surrounded by water
A working cycle of a gasoline engine consists of four strokes, which reduces the temperature of the cylinder block. There is a water tank outside the cylinder, which makes the cylinder surrounded by water. This is to reduce the internal energy of the cylinder by means of ()

This is to reduce the internal energy of the cylinder by (heat transfer)

The principle of cross phase multiplication

There seems to be a formula, but I don't know how to deduce it
X2 is the square of X, which is indicated here
Bivariate agenda:
X2+（q+p)X+(q.p)=0
It is represented by cross multiplication
（X+q)(X+p)=0

Find the general solution of the total differential equation (3x & # 178; + 6xy & # 178;) DX + (6x & # 178; y + 4Y & # 178;) dy = 0
Use curve integral to solve!

DX + (6x; (3x; (3x; (3x; (; (3x; (; (3x; (; (3x; (178; (6xy; (178;; + 6xy; (178; + 6xy; (178; + 6xy; (178;; (6x; (178; y + 4Y; (178; y + 4Y; (178; 178; y + 4Y; (178; Y; (178; y + 4Y; (178; 178; Y; (178; Y; (178; Y; (Y; (178; 178; 178; Y; (178; 178; 178; 178; y 65\; (178; (178; (178; (178; \\353535^ 3 / 3 = C

How many tons is a cubic meter of steam produced by a boiler!

Steam has special characteristics, which are divided into saturated steam and superheated steam. Generally, we usually use saturated steam. The quality of saturated steam is related to its pressure and temperature. For saturated steam, when the pressure is fixed, its temperature is also a fixed value. You lack parameters here, I can only provide you with a small part of saturated steam data: 1

What are the multiplication formulas in junior high school? Different books are different. What is it?

Complete square: (a + b) square = a square + b square + 2Ab
(a-b) square = a square + b square - 2Ab
Square difference: a square - b square = (a + b) (a-b)
Cubic sum
The cubic difference is generally not required