`\qquad (x+3)(x-10)=1-x(x-9)`
`<=> x^2-10x+3x-30=1-x^2+9x`
`<=> x^2-7x-30=-x^2+9x+1`
`<=> x^2-7x-30+x^2-9x-1=0`
`<=> 2x^2-16x-31=0`
`<=> x^2-8x-31/2=0`
`<=> x^2-8x+16=63/2`
`<=> (x-4)^2=63/2`
`<=>`\(\left[ \begin{array}{l}x-4=\dfrac{3\sqrt{14}}{2}\\x-4=\dfrac{-3\sqrt{14}}{2}\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{8+3\sqrt{14}}{2}\\x=\dfrac{8-3\sqrt{14}}{2}\end{array} \right.\)
Vậy `S={(8+-3\sqrt{14})/2}`
