f(x)=-3x^2+2x+7
\Delta=b^2-4ac=2^2-4*(-3)*7=4+82=88
\sqrt{\Delta}=\sqrt{88}=\sqrt{4*22}=2\sqrt{22}
x_1=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-2-2\sqrt{22}}{-6}=\frac{1+\sqrt{22}}{3}
x_2=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-2+2\sqrt{22}}{-6}=\frac{1-\sqrt{22}}{3}
f)
f(x)=2x^2-12x+16
\Delta=144-4*2*16=144-128=16
\sqrt{\Delta}=4
x_1=\frac{12-4}{4}=2
x_2=\frac{12+4}{4}=4