What is the explanation of the equation (x-4 / X-5) + (X-8 / X-9) = (X-7 / X-8) + (X-5 / X-6),

What is the explanation of the equation (x-4 / X-5) + (X-8 / X-9) = (X-7 / X-8) + (X-5 / X-6),

(x-4/x-5)+(x-5/x-6)=(x-8/x-9)+(x-7/x-8)
-1/x2-11x+30=-1/x2-17x+72
x=7
The top two is the square

Solving the equation: 2x + | x | = 8, how can X be equal to 8

I have just answered the main question. Please refer to the comments on the original topic for details
：“|x|=8-2x
x> If x = 0, then x = 8-2x, so 3x = 8, x = 8 / 3
x

3. - 5, - 11 and 7 are 24

[-5-（-11）]*(7-3)

Seeking 50 calculation questions in fifth grade volume I

6.9 + 4.8 + 3.10.456 + 6.22 + 3.7815.89 + (6.75-5.89) 4.02 + 5.4 + 0.985.17-1.8-3.213.75 - (3.75 + 6.48) 3.68 + 7.56-2.687.85 + 2.34-0.85 + 4.6635.6-1.8-15.6-7.23.82 + 2.9 + 0

As shown in the figure, in trapezoidal ABCD, bisectors of ∠ ABC and ∠ DCB intersect at a point P on trapezoidal median EF, pH ⊥ AB at h, if EF = 3, pH = 1, then the area of trapezoidal ABCD, thank you for the process

From the median EF = 3, AD + BC = 6 can be obtained
Then the bisectors of ∠ ABC and ∠ DCB intersect at a point P on the trapezoidal median EF
The results show that EP = be = 1 / 2Ab, EF = FC = 1 / 2dc
Then AB + DC = 2 (be + FC) = 2 (EP + EF) = 2 × 3 = 6
Then the circumference of ladder ABCD is: 6 + 6 = 12

We know the relation between the two roots of the quadratic equation (mx-n) - 2 = 0 (m ≠ 0) with respect to x 1 = 1, X2 = 2 (1) m, n
It is known that the two roots of the quadratic equation (mx-n) - 2 = 0 (m ≠ 0) with respect to X are X1 = 1, X2 = 2
(1) The relationship between M and n
(2) M = 1, the above equation is written in the general form of quadratic equation with one variable
It's better to be more careful in the process of grade two

(1) Substituting X1 = 1 into the equation, m-n-2 = 0, that is, M-N = 2
Substituting x2 = 2 into the equation, 2m-n-2 = 0, that is 2m-n = 2
Compared with ① and ②, 2m = m, that is, M = 0, so n = 2
(2) Substitute M = 1 into the equation, that is, x-n-2 = 0

Cuboid, cube, cylinder, cone volume, surface area and volume formula derivation process
There are cuboid, cube, cylinder, cone, there are several points, lines, surface

Cuboid: v = a · B · H = s base · height, s table = (a · B + B · C + a · C) · 2 P · s · no need to deduce formula, square: v = A & # 179; = s base · height, s table = 6 · a & # 178; P · s · no need to deduce formula, cylinder: v = π R & # 178; · h table = 2 π R & # 178; + 2 π R · H = 2 π R · (R + H) P · s · see circular deduction

The perimeter of a rectangular grassland is 42 meters, and the length is twice the width. How many square meters is the area of this grassland?

42 △ 2 = sum of length and width of 21 M
21 ÷ (1 + 2) = 7m wide
2 × 7 = 14m long
7 × 14 = 98 square meters

The accuracy and significant number of approximate number 0.0125 are pointed out, and the maximum significant number is x, and the square of (a + 2) and the absolute value of a + B + 5 are opposite to each other,
Find the value of the square B of 3A - [the square B of 2A - (the square B of 2ab-a) - the square of 4A] - XAB

From the meaning (a + 2) = 0 (a + B + 5) = 0, can you do it

It takes 28.5 seconds for a train to pass through a 640 meter long tunnel with a speed of 108 km / h. The body length of the train is calculated

The length of the train is set as X meters
Method 1
108 km/h = 30m/s
640 + x = 30 × 28.5
x = 215 m
Method 2
108 km/h = 30m/s
640/30 = 64/3 s
x = 30 × (28.5 - 64/3)
= 215 m