Question

Tìm x, biết:

a, (3x-1) (2x+7) - (x+1) (6x-5) = 16

b, (10x+9) . x - (5x-1) (x+3) = 8

GIÚP MÌNH VỚI

Answer 1

`a) (3x-1) (2x+7) - (x+1) (6x-5) = 16`

`6x^2 + 21x -2x -7 - (6x^2 -5x+6x-5) =16`

`<=> 6x^2 +19x -7- 6x^2 +5x -6x +5 =16`

`<=> 18x -2 =16`

`<=>18x =18`

`=> x =18/18 =1`

` (10x+9) . x - (5x-1) (x+3) = 8`

`<=> 10x^2 +9x - (5x^2 +15x -x-3) =8`

`<=> 10x^2 +9x -5x^2 -15x +x+3 =8`

`<=> 5x^2 -5x +3 -8 =0`

`<=> 5x^2 -5x -5 =0`

`<=> x^2 -x -1 =0`

`=> Delta = (-1)^2 -4*1*(-1) =5 >0`

`\(\Rightarrow x=\dfrac{-b\pm\sqrt{\Delta}}{2a}=\dfrac{-\left(-1\right)\pm5}{2\cdot1}=\dfrac{1\pm\sqrt{5}}{2}\)

Vậy \(S=\left\{\dfrac{1\pm\sqrt{5}}{2}\right\}\)