Đáp án:
b) `x( 5 - 2x) + 2x( x -1) = 13`
`=> 5x - 2x^2 + 2x^2 - 2x =13`
`=> 3x = 13`
`=> x = 13/3`
`S= {13/3}`
d) `3x ( 2x+ 3) - ( 2x + 5)( 3x -2) = 8`
`=> 6x^2 + 9x - 6x^2 + 4x - 15x + 10 =8`
`=> -2x = 8 - 10`
`=> -2x = -2`
`=> x =1`
`S = {1}`
f) `2x( 6x -2x^2) + 3x^2 ( x -4) =8`
`=> 12x^2 - 4x^3 + 3x^3 - 12x^2 =8`
`=> -x^3 = 8`
`=> x^3 = -8`
`=> x = -2`
`S={-2}`
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