tìm x , bt: a , 3x . (12x -4) - 9x . ( 4x -3) = 30 b , x . (5 - 2x) + 2x ( x - 1) = 15 c , 6x . (5x + 3) + 3x . (1 - 10x) = 7

`a . ` `3x.(12x-4)- 9x.(4x -3)=30 `

`<=>` `36x-12x-36x+27x=30`

`<=>` `15x=30`

`<=>` `x=30:15`

`<=>` `x=2`

Vậy `x=2`

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`b . ` ` x.(5-2x)+2x.( x - 1)=15`

`<=>` `5x-2x^2+2x^2-2x=15`

`<=>` `3x=15`

`<=>` `x=15:3`

`<=>` `x=5`

Vậy `x=5`

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`c . ` `6x.(5x+3)+3x.(1-10x)=7`

`<=>` `30x^2+18x+3x-30x^2=7`

`<=>` `21x=7`

`<=>` `x=7:21`

`<=>` `x=1/3`

Vậy `x=1/3`

`\text{#slaywithme}`