How do you solve x^2 + 8x=0 using the quadratic formula?

1 Answer
Aug 28, 2017

See a solution process below:

Explanation:

We can rewrite the equation in standard form as:

x^2 + 8x + 0 = 0

Now, we can use the quadratic equation to solve this problem:

The quadratic formula states:

For color(red)(a)x^2 + color(blue)(b)x + color(green)(c) = 0, the values of x which are the solutions to the equation are given by:

x = (-color(blue)(b) +- sqrt(color(blue)(b)^2 - (4color(red)(a)color(green)(c))))/(2 * color(red)(a))

Substituting:

color(red)(1) for color(red)(a)

color(blue)(8) for color(blue)(b)

color(green)(0) for color(green)(c) gives:

x = (-color(blue)(8) +- sqrt(color(blue)(8)^2 - (4 * color(red)(1) * color(green)(0))))/(2 * color(red)(1))

x = (-color(blue)(8) +- sqrt(64 - 0))/2

x = (-color(blue)(8) +- sqrt(64))/2

x = (-color(blue)(8) - 8)/2 and x = (-color(blue)(8) + 8)/2

x = -16/2 and x = 0/2

x = -8 and x = 0

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A simple way to solve this equation without the quadratic is to factor an x out of each term on the left side of the equation:

x(x + 8) = 0

Then solve each term on the left for 0:

Solution 1:

x = 0

Solution 2:

x + 8 = 0

x + 8 - color(red)(8) = 0 - color(red)(8)

x + 0 = -8

x = -8