Solve the equation by the quadratic formula.
-$$x ^ { 2 } + 12 x + 21 = 0$$
A) $$6 \pm \sqrt { 21 }$$
B) $$6 + \sqrt { 15 }$$
C) $$- 12 + \sqrt { 21 }$$
D) $$- 6 \pm \sqrt { 15 }$$

Question

Quizplus · Accepted Answer

The quadratic formula is $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$ for a quadratic equation $ax^2 + bx + c = 0$. Here, $a = 1$, $b = 12$, and $c = 21$. Plugging these into the formula gives $$x = \frac{-12 \pm \sqrt{(12)^2 - 4(1)(21)}}{2(1)} = \frac{-12 \pm \sqrt{144 - 84}}{2} = \frac{-12 \pm \sqrt{60}}{2} = -6 \pm \sqrt{15}$$.

Solve the Equation by the Quadratic Formula x2+12x+21=0x ^ { 2 } + 12 x + 21 = 0x2+12x+21=0

Solve the Equation by the Quadratic Formula $x ^ { 2 } + 12 x + 21 = 0$