Question

For the function f(x) = x2 + 11x + 20, find when f(x) = −8

Answer 1

Okay, here we have this:

`x^2+11x+20=-8`

Let's solve it:

`x^2+11x+28=0`

We are going to solve with the general formula for equations of the second degree:

`x_(1,2)=\frac{-11\pm\sqrt[]{11^2-4\cdot1\cdot28}}{2\cdot1}`
`\begin{gathered} =\frac{-11\pm\sqrt[]{121-112}}{2} \\ =\frac{-11\pm\sqrt[]{9}}{2} \\ =(-11\pm3)/(2) \\ x_1=(-11+3)/(2)=(-8)/(2)=-4 \\ x_{2_{}}=(-11-3)/(2)=(-14)/(2)=-7 \end{gathered}`

Finally we obtain that the solutions to the equation x²+11x+20=-8 are x=-4 and x=-7.