`a) 2x^2-98x=0`
`<=> 2x(x^2-49)=0`
`<=> 2x(x^2-49)=0`
`<=> 2x(x-7)(x+7)=0`
`<=>`\(\left[ \begin{array}{l}x=0\\x-7=0\\x+7=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0\\x=7\\x=-7\end{array} \right.\)
`b) (2x-3)(4x^2+6x+9)-8x(x-3)(x+3)=2x+8`
`<=> 8x^3-27-8x(x^2-9)-2x-8=0`
`<=> 8x^3-27-8x^3+72x-2x-8=0`
`<=> 70x-35=0`
`<=> 2x-1=0`
`<=> x=1/2`