I need help with solving for (x+4)*x=15.5

Question

anonymous · Answer

Hello, distribute the x to the terms in parenthesis, subtract 15.5 from both sides and then use the quadratic formula?

anonymous · Answer

I'm not sure what the quadratic formula. Is can you explain?

anonymous · Answer

$$ax^2 + bx + c = 0$$
$$x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$$

anonymous · Answer

Firstly get all of your values on one side and zero on the other

anonymous · Answer

I'm in 7th grade. Are you in high school? ...because you lost me. What is a, b, or c

whpalmer4 · Answer

The quadratic formula gives you the solution for an equation $ax^2+bx+c=0, a\ne0$.

anonymous · Answer

In my case which number is a, b, c

whpalmer4 · Answer

$$(x+4)*x=15.5$$$$x^2+4x=15.5$$You could complete the square by taking half the coefficient of the $x$ term, squaring it, and adding to both sides:$$x^2+4x+(\frac{4}{2})^2=15.5+(\frac{4}{2})^2$$Now rewrite the left hand side as a square:$$(x+2)^2=15.5+4=19.5$$Take the square root of both sides$$(x+2)=\pm\sqrt{19.5}\approx \pm4.416$$
Solve for x$$x=-2\pm4.416 $$$$x=2.416, x = -6.416$$
$a$ is the coefficient of the $x^2$ term, 1 in your case. $b$ is the coefficient of the $x$ term, 4 in your case.  $c$ I hope you can figure out :-)

whpalmer4 · Answer

You have to put your equation in the right form before you can apply the formula.  In this case that means distributing $x$ as in the 2nd line of my post where I solve the equation.

whpalmer4 · Answer

And if using the quadratic formula, you would want the equation to read
$$x^2+4x-15.5=0$$giving $a=1, b=4, c=-15.5$.

anonymous · Answer

Thank You