Question

Tìm x, biết:

a) 16x²-(4x-5)²=15                     b) (2x+1)(1-2x)+(1-2x)²=18

c) (x-5)²-x(x-4)=9                        d) (x-5)²+(x-4)(1-x)=0

Answer 1

a) <=> (4x - 4x + 5)(4x + 4x - 5) = 15 <=> 40x = 15 <=> x = 3/8

Answer 2

a) <=> (4x - 4x + 5)(4x + 4x - 5) = 15 <=> 5(8x-5) = 15

<=> 40x = 40 <=> x = 1

Cái này mới chuẩn

Answer 3

b) (2x+1)(1-2x)+(1-2x)²=18 <=> 1 - 4x² + 4x² - 4x + 1 = 18

<=> -4x = 16 <=> x = -4

Answer 4

c) (x-5)²-x(x-4)=9 <=> x^2 - 10x + 25 - x^2 + 4x = 9

<=> -6x = -16 <=> x = 8/3

Answer 5

d) (x-5)²+(x-4)(1-x)=0

<=> x^2 - 10x + 25 - x^2 + 5x - 4 = 0<=> -5x = -21 <=> x = 21/5

Answer 6

a: Ta có: \(16x^2-\left(4x-5\right)^2=15\)

\(\Leftrightarrow16x^2-16x^2+40x-25=15\)

\(\Leftrightarrow40x=40\)

hay x=1

b: Ta có: \(\left(1+2x\right)\left(1-2x\right)+\left(1-2x\right)^2=18\)

\(\Leftrightarrow1-4x^2+4x^2-4x+1=18\)

\(\Leftrightarrow-4x=16\)

hay x=-4

c: Ta có: \(\left(x-5\right)^2-x\left(x-4\right)=9\)

\(\Leftrightarrow x^2-10x+25-x^2+4x=9\)

\(\Leftrightarrow-6x=-16\)

hay \(x=\dfrac{8}{3}\)