Question

x²-12x-12=0 tìm x

Answer 1

`x^2 -12x -12 =0`

`=> Delta = (-12)^2 -4*1*(-12) = 192 >0`

`=> PT` có `2` nghiệm`

`=>`\(\left\{{}\begin{matrix}x_1=\dfrac{-b+\sqrt{\Delta}}{2a}=\dfrac{-\left(-12\right)+\sqrt{192}}{2\cdot1}\\x_2=\dfrac{-b-\sqrt{\Delta}}{2a}=\dfrac{-\left(-12\right)-\sqrt{192}}{2\cdot1}\end{matrix}\right.\)

`<=>`\(\left\{{}\begin{matrix}x_1=\dfrac{2\cdot6+2\cdot4\cdot\sqrt{3}}{2}=6+4\sqrt{3}\\x_2=\dfrac{2\cdot6+2\cdot4\cdot\sqrt{3}}{2}=6-4\sqrt{3}\end{matrix}\right.\)

Vậy `S={ 6 +- 4sqrt{3} }`