Phân tích đa thức thành nhân tử x⁴ +x³ +2x² +x +1 Tìm x biết 4x² -3x -1 =0

a. (-2x+3)² – (3y)²

b. (-2x)² – (y–x)²

P = x² - 2x + 5 = x² - 2x + 1 + 4

   = ( x - 2 )² + 1 ≥ 1 ( vì ( x - 2 )² ≥ 0 )

Dấu " = " xảy ra khi x - 2 = 0 => x = 2

Vậy GTNN của P là 1 khi x = 2

4.A

5.D

   (5x - 2)² - (2x - 1)²

= (5x - 2 + 2x - 1) (5x - 2 - 2x + 1)

= (7x - 3) (3x - 1)

1.The facsimile was invited by Alexander Bain in 1843.

2.The beans are dried in the sun.

3.Payment can be made at any post office.

4.How is English learned?

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6.Where are these photograghs taken?

7.The students being shown around the factory by the foreman.

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10.The room were being cleaned when I arrived.

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D

b) ( x - √7y )² = x² - 2x.7y + ( √7y )² 

= x² - 14xy + 7y

     4 (x - 5) - 2³ = 2⁴*3

=> 4 (x - 5) - 2³ = 16*3 = 48

=> 4 (x - 5) = 48 + 2³ = 48 + 8 = 56

=> x - 5 = 56/4 = 14

=> x = 14 + 5 = 19

 Vậy x = 19