Question

Find the quadratic equation whose roots are $9-\sqrt{5},9+\sqrt{5}$

• A. $x^2-18x-56=0$
• B. $x^2+18x+56=0$
• C. $4x^2-72x-56=0$
• D. $x^2-18x+56=0$

Answer 1

The correct option is D $x^2-18x+56=0$

$(x-(9-\sqrt{5}))(x-(9+\sqrt{5}))=0$
$x^2-9x-\sqrt{5x}-9x+\sqrt{5x}+81-25=0$
$x^2-18x+56=0$