[tex]-3x^{2}+30x-90=0 \\ \\ x^{2}-10x+30=0 \\ \\ \Delta=(-10)^{2}-4*1*30=100-20=-20 \\ \\ \sqrt{\Delta}= \sqrt{-20}=i \sqrt{20} =2i \sqrt{5} \\ \\ x_{1}= \frac{10-2i \sqrt{5} }{2} = 5-i \sqrt{5} \\ \\ x_{2}= \frac{10+2i \sqrt{5} }{2} = 5+i \sqrt{5} [/tex]
