Question
Solve the following quadratic equation using formula method only
$x^2 - 4x - 1 = 0$
$x^2 - 4x - 1 = 0$
✓
Answer
$x^2-4 x-1=0 $
$ a=1 ; b=-4 ; c=-1$
$ D=b^2-4 a c $
$ =(-4)^2-4(1)(-1) $
$ =16+4 $
$=20 $
$x=\frac{-b \pm \sqrt{b^2-4 a c}}{2 a} $
$x=\frac{4 \pm \sqrt{20}}{2} $
$ x=\frac{4 \pm 2 \sqrt{5}}{2} $
$x=2+\sqrt{5}, x=2-\sqrt{5}$
$ a=1 ; b=-4 ; c=-1$
$ D=b^2-4 a c $
$ =(-4)^2-4(1)(-1) $
$ =16+4 $
$=20 $
$x=\frac{-b \pm \sqrt{b^2-4 a c}}{2 a} $
$x=\frac{4 \pm \sqrt{20}}{2} $
$ x=\frac{4 \pm 2 \sqrt{5}}{2} $
$x=2+\sqrt{5}, x=2-\sqrt{5}$
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