`a, 3(x+2)-6(x-5)=2(5-2x)`
`↔3x+6-6x+30=10-4x`
`↔3x-6x+4x=10-30-6`
`↔x=-26`
Vậy `x=-26`
`b, (-2x)·(-4x)+28=100`
`↔8x^2+28=100`
`↔8x^2=72`
`↔x^2=9`
`↔x=±3`
Vậy `x=±3`
`c, 5x·(-x)^2+1=6`
`↔5x^3=5`
`↔x^3=1`
`↔x=1`
Vậy `x=1`
`d, 3x^2+12x=0`
`↔3x(x+4)=0`
`↔`\(\left[ \begin{array}{l}3x=0\\x+4=0\end{array} \right.\)
`↔`\(\left[ \begin{array}{l}x=0\\x=-4\end{array} \right.\)
Vậy `x=0` hoặc `x=-4`
