Given that ab ≠ 0, the sufficient and necessary condition for a + B = 1 is A3 + B3 + ab-a2-b2 = 0

Given that ab ≠ 0, the sufficient and necessary condition for a + B = 1 is A3 + B3 + ab-a2-b2 = 0

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In △ ABC, ab = AC, take a point D on AB, take a point E on the extension line of AC, make BD = CE, connect De to BC at point F, and prove: DF = EF

Make DG ‖ AE, DG cross BC to g
∵DG‖AE
∴∠DGB=∠ACB
And ∵ ∠ CGD = 180 ° - DGB, ∠ BCE = 180 ° - ACB
∴∠CGD=∠BCE
∵∠B=∠ACB,∠DGB=∠ACB
∴∠B=∠DGB
∴BD=GD
And ∵ BD = CE
∴GD=CE
And ∵ ∠ BFD = ∠ CFE
∴ΔDFG≌ΔEFC
∴DF=EF

2.5 times of a number is equal to 8 / 5 of 40

∵ 2.5 times of a number is equal to 8 / 5 of 40, and the number is: 40 * 8 / 5 △ 2.5 = 64 △ 2.5 = 25.6

The school playground used to be a square. Now it extends 20 meters to the East and 6 meters to the south. The area increases by 900 square meters. How long is the original playground
Additional questions

Let the side length of a square be x, then (x + 6) (x + 20) = x2 + 900, X2 + 20x + 6x + 120 = x2 + 900, 26x = 780

The length of the base of an isosceles triangle is 10 cm. If the difference between the two parts is 3 cm, the waist length is 10 cm______ ．

As shown in the figure, let the waist length of an isosceles triangle be xcm. When the difference between AD + AC and BC + BD is 3cm, that is 12x + X - (12x + 10) = 3, the solution is x = 13cm; when the difference between BC + BD and AD + AC is 3cm, that is 10 + 12x - (12x + x) = 3, the solution is x = 7cm. Therefore, the waist length is 7cm or 13cm

Calculate 2A (A-3) ^ 1-6a ^ 2 (3-A) - 8A (A-3)

2a(a-3)^1-6a^2(3-a)-8a(a-3)
=2a(a-3)+6a^2(a-3)-8a(a-3)
=2a(a-3)（1+3a-4）
=2a(a-3)(3a-3)
=6A (A-3) (A-1) --- this is the factorization
=6A ^ 3-24a ^ 2 + 18a --- this is the result

As shown in the figure, this is a triangle shaped pattern composed of several potted flowers. Each side (including two vertices) has n (n > 1) disk flowers, and the total number of flowers in each pattern pot
The number is s
○ ○ ○
○ ○ ○ ○ ○ ○
n=2,s=2 ○ ○ ○ ○ ○
n=3,s=6 ○ ○ ○ ○
n=4,s=9
What is the relationship between S and N?

s=3*n-3

Common plants in Section 3 of science seventh grade homework B
Like the title,
To all ah, all written, I add points

Multiple choice: 1. B 2. A 3. D 4. C 5. B 6. D

If M = x3-3x2y + 2xy2 + 3y2, n = x3-2x2y + xy2-5y3, then 2x3-7x2y + 5xy2 + 14y2 equals ()
If M = x3-3x2y + 2xy2 + 3y2, n = x3-2x2y + xy2-5y3, then 2x3-7x2y + 5xy2 + 14y2 equals ()
The space is represented by letters

3m-n
=3(x³-3x²y+2xy²+3y²)-(x³-2x²y+xy²-5y²)
=3x³-9x²y+6xy²+9y²-x³+2x²y-xy²+5y²
=2x³-7x²y+5xy²+14y²
therefore
2x³-7x²y+5xy²+14y²=3m-n

Yinghua primary school has a rectangular playground with a length of 120 meters and a width of 80 meters. It is drawn on a plan with a scale of 1:4000. How many centimeters should be drawn for the length and width?

120 m = 12000 cm, 80 m = 8000 cm, 12000 × 14000 = 3 (CM), 8000 × 14000 = 2 (CM); answer: length and width should be 3 cm and 2 cm respectively