Question

Which of the following is a solution of x2 + 2x + 8?

Answer 1

A solution of a quadratic equation (ax^2+bx+c) is the point at which the parabola crosses the x-axis. We can find this by using the Quadratic formula, which is
`(-b+- √(b^2-4ac) )/(2a)`. We can solve the equation as follows:


`(-b+- √(b^2-4ac) )/(2a) \\ (-2+- √(2^2-4(1)(8)) )/(2(1)) \\ (-2+- √(4-32) )/(2) \\ (-2+- √(-28) )/(2)`
Then we separate the negative from -28 to get:

`(-2+- √(28)* √(-1) )/(2)=(-2+-2i √(7) )/(2)`
Then we continue to solve by factoring common terms (-2 and 2). We get the solutions of
`-1+i √(7) \\ or \\ -1-i √(7)`. Choice B matches our first solution.

:)