How do you set up the quadratic formula with the correct numbers? x² - 4x - 15 = 0

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How do you set up the quadratic formula with the correct numbers? x² - 4x - 15 = 0

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Answer 1 · 2018-06-07T14:02:07

$x = \frac{4 + \sqrt{76}}{2} or \frac{4 - \sqrt{76}}{2}$ $x = (4 + sqrt(76))/2 or (4 - sqrt(76))/2$

Explanation:

$x^{2} - 4 x - 15 = 0$ $x^2 - 4x - 15 = 0$

Recall;

$a x^{2} + b x + c = 0$ $ax^2 + bx + c = 0$

Comparing you will have;

$a = 1$ $a = 1$

$b = - 4$ $b = -4$

$c = - 15$ $c = -15$

Using Quadratic Formula;

$x = \frac{- b \pm \sqrt{b^{2} - 4 a c}}{2 a}$ $x = (-b +- sqrt(b^2 - 4ac))/(2a)$

Plugging the values into the equation..

$x = \frac{- (- 4) \pm \sqrt{{(- 4)}^{2} - 4 (1) (- 15)}}{2 (1)}$ $x = (-(-4) +- sqrt((-4)^2 - 4(1)(-15)))/(2(1))$

$x = \frac{4 \pm \sqrt{16 + 60}}{2}$ $x = (4 +- sqrt(16 + 60))/2$

$x = \frac{4 \pm \sqrt{76}}{2}$ $x = (4 +- sqrt(76))/2$

$x = \frac{4 + \sqrt{76}}{2} or \frac{4 - \sqrt{76}}{2}$ $x = (4 + sqrt(76))/2 or (4 - sqrt(76))/2$

Answer 2 · 2018-06-07T14:08:38

$see explanation$ $"see explanation"$

Explanation:

$the solution of a quadratic equation in standard form$ $"the solution of a quadratic equation in "color(blue)"standard form"$

$∙ x a x^{2} + b x + c = 0; a \neq 0$ $•color(white)(x)ax^2+bx+c=0;a!=0$

$can be solved using the quadratic formula$ $"can be solved using the "color(blue)"quadratic formula"$

$∙ x x = \frac{- b \pm \sqrt{b^{2} - 4 a c}}{2 a}$ $•color(white)(x)x=(-b+-sqrt(b^2-4ac))/(2a)$

$x^{2} - 4 x - 15 = 0 is in standard form$ $x^2-4x-15=0" is in standard form"$

$with a = 1, b = - 4 and c = - 15$ $"with "a=1,b=-4" and "c=-15$

$x = \frac{- (- 4) \pm \sqrt{{(- 4)}^{2} - (4 \times 1 \times - 15)}}{2 \times 1}$ $x=(-(-4)+-sqrt((-4)^2-(4xx1xx-15)))/(2xx1)$

$x = \frac{4 \pm \sqrt{16 + 60}}{2}$ $color(white)(x)=(4+-sqrt(16+60))/2$

$x = \frac{4 \pm \sqrt{76}}{2} = \frac{4 \pm 2 \sqrt{19}}{2} = 2 \pm \sqrt{19}$ $color(white)(x)=(4+-sqrt76)/2=(4+-2sqrt19)/2=2+-sqrt19$

$x \approx - 2.36 or x \approx 6.36 to 2 dec. places$ $x~~-2.36" or "x~~6.36" to 2 dec. places"$

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How do you set up the quadratic formula with the correct numbers? x² - 4x - 15 = 0

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