Question

Which equation shows the quadratic formula used correctly to solve 7x2 = 9 + x for x? X = StartFraction negative 1 plus-or-minus StartRoot (negative 1) squared minus 4 (7) (9) EndRoot Over 2 (7) EndFraction x = StartFraction 1 plus-or-minus StartRoot (negative 1) squared minus 4 (7) (9) EndRoot Over 2 (7) EndFraction x = StartFraction negative 1 plus-or-minus StartRoot (negative 1) squared +4 (7) (9) EndRoot Over 2 (7) EndFraction x = StartFraction 1 plus-or-minus StartRoot (negative 1) squared +4 (7) (9) EndRoot Over 2 (7) EndFraction

Answer 1

Answer:

$x=\dfrac{-(-1)\pm \sqrt{(-1)^{2}-4(7)(-9)}}{2(7)}$

Step-by-step explanation:

The quadratic equation is as follows :

$7x^2=9+x$ ...(1)

The solution of a quadratic equation $ax^2+bx+c=0$ is given by :

$x=\dfrac{-b\pm \sqrt{b^2-4ac} }{2a}$

Equation (1) can also be written as follows :

$7x^2-9-x=0\\\\7x^2-x-9=0$

Here, a = 7, b = -1 and c = -9

$x=\dfrac{-b+ \sqrt{b^2-4ac} }{2a}, x=\dfrac{-b-\sqrt{b^2-4ac} }{2a}\\\\x=\dfrac{-(-1)+\sqrt{(-1)^{2}-4(7)(-9)}}{2(7)}, \dfrac{-(-1)-\sqrt{(-1)^{2}-4(7)(-9)}}{2(7)}\\\\x=1.20\ s, -1.06\ s$

Neglecting negative value.

So, it will hit the ground in 1.2 s.