Question

tìm x :

1)25x²-1=0

2)x²-4x=0

3)x.(x-4)+2x-3=0

4) (x+4)²-(x+2).(x-2)=10-2x

5)x²-4x=0

6)(2x-1)²-4x²+1=0

Answer 1

1) 25x² - 1 = 0

(5x)² - 1² = 0

(5x - 1)(5x + 1) = 0

5x - 1 = 0 hoặc 5x + 1 = 0

*) 5x - 1 = 0

5x = 1

x = 1/5

*) 5x + 1 = 0

5x = -1

x = -1/5

Vậy x = -1/5; x = 1/5

2) x² - 4x = 0

x(x - 4) = 0

x = 0 hoặc x - 4 = 0

*) x - 4 = 0

x = 4

Vậy x = 0; x = 4

3) x(x - 4) + 2x - 3 = 0

x² - 4x + 2x - 3 = 0

x² - 2x - 3 = 0

x² + x - 3x - 3 = 0

(x² + x) - (3x + 3) = 0

x(x + 1) - 3(x + 1) = 0

(x + 1)(x - 3) = 0

x + 1 = 0 hoặc x - 3 = 0

*) x + 1 = 0

x = -1

*) x - 3 = 0

x = 3

Vậy x = -1; x = 3

4) (x + 4)² - (x - 2)(x + 2) = 10 - 2x

x² + 8x + 16 - x² + 4 = 10 - 2x

8x + 2x = 10 - 16 - 4

10x = -10

x = -10 : 10

x = -1

5) Câu này đã làm ở câu 2

6) (2x - 1)² - 4x² + 1 = 0

(2x - 1)² - (4x² - 1) = 0

(2x - 1)² - (2x - 1)(2x + 1) = 0

(2x - 1)(2x - 1 - 2x - 1) = 0

(2x - 1).(-2) = 0

2x - 1 = 0

2x = 1

x = 1/2

Answer 2

1: =>(5x-1)(5x+1)=0

=>x=1/5 hoặc x=-1/5

2: =>x(x-4)=0

=>x=0 hoặc x=4

3: =>x^2-4x+2x-3=0

=>x^2-2x-3=0

=>(x-3)(x+1)=0

=>x=3 hoặc x=-1

4: =>x^2+8x+16-x^2+4=10-2x

=>8x+20=10-2x

=>10x=-10

=>x=-1

5: =>x(x-4)=0

=>x=0 hoặc x=4

6: =>4x^2-4x+1-4x^2+1=0

=>-4x+2=0

=>-4x=-2

=>x=1/2