[tex]a)\\\\x^2+9=6x\\x^2-6x+9=0\\\Delta=(-6)^2-4*1*9\\\Delta=36-36=0\\x_0=\frac{-b}{2a}\to\frac{6}{2}=3\\\\[/tex]
[tex]b)\\\\3x^2+2\sqrt{15}x+5=0\\\Delta=(2\sqrt{15})^2-4*3*5=60-60=0\\x_0=\frac{-b}{2a} \to \frac{-2\sqrt{15}}{6}=-\frac{\sqrt{15}}3[/tex]
[tex]c)\\\\(2-x)(2+x)=x^2+4\sqrt2x+8\\2^2-x^2=x^2+4\sqrt2x+8\\4-x^2=x^2+4\sqrt2x+8\\0=x^2+x^2+4\sqrt2x+8-4\\2x^2+4\sqrt2x+4=0\\\\\Delta=(4\sqrt2)^2-4*2*4=32-32=0\\\\x_0=\frac{-b}{2a} \to \frac{-4\sqrt2}4=-\sqrt2[/tex]
