Question

Which equation shows the quadratic formula used correctly to solve 7x2 = 9 + x for x?

Answer 1

The equation should be 7x^2 -x-9=0

Answer 2

Answer:

The equation $x=\frac{-(-1)\pm \sqrt{(-1)^2-4(7)(-9)}}{2(7)}$ shows the quadratic formula used correctly to solve the given equation.

Step-by-step explanation:

If a quadratic equation is defined as $ax^2+bx+c=0$, then the quadratic formula is

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

The given equation is

$7x^2=9+x$

Subtract 9 and x from both the sides.

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

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

Substitute  a=7, b=-1 and c=-9 in the quadratic formula.

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

Therefore the equation $x=\frac{-(-1)\pm \sqrt{(-1)^2-4(7)(-9)}}{2(7)}$ shows the quadratic formula used correctly to solve the given equation.