Answer:
[tex]4\pm\sqrt{19}[/tex]
Step-by-step explanation:
[tex]x^2-8x=3\\x^2-8x-3=0\\x^2-8x+16-19=0\\(x-4)^2-19=0\\(x-4-\sqrt{19})(x-4+\sqrt{19})=0\\x=4\pm\sqrt{19}[/tex]