a) \sqrt2-1=(\sqrt2-3x)(\sqrt2+4)
\sqrt2-1=2+4\sqrt2-3\sqrt2x-12x
12x+3\sqrt2x=2+4\sqrt2-\sqrt2+1
3x(4+\sqrt2)=3+3\sqrt2|:3
x(4+\sqrt2)=1+\sqrt2
x=\frac{1+\sqrt2}{4+\sqrt2}=\frac{(1+\sqrt2)(4-\sqrt2)}{(4+\sqrt2)(4-\sqrt2)}
x=\frac{4-\sqrt2+4\sqrt2-2}{16-2}
x=\frac{3\sqrt2+2}{14}
b)
x-3=x\sqrt2-3\sqrt3
x-x\sqrt2=3-3\sqrt3
x(1-\sqrt2)=3-3\sqrt3
x=\frac{3-3\sqrt3}{1-\sqrt2}=\frac{3-3\sqrt3}{1-\sqrt2}*\frac{1+\sqrt2}{1+\sqrt2}
x=\frac{3+3\sqrt2-3\sqrt3-3\sqrt6}{-1}
x=3\sqrt6+3\sqrt3-3\sqrt2-3
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x=3(\sqrt6+\sqrt3-\sqrt2-1)