SOLUTION: I am trying to work the following problem, but am unsure how to go about doing so. Find all values of x if f(x)=-38: f(x)=5x+21/x This is what I have gotten so far: f(x

Question 145362: I am trying to work the following problem, but am unsure how to go about doing so.
Find all values of x if f(x)=-38:
f(x)=5x+21/x
This is what I have gotten so far:
f(x)=5(-38)+[21/(-38)]
f(x)=-190+(21/-38)
What do I do from here?
Answer by vleith(2983) (Show Source): You can put this solution on YOUR website!
Find all values of x if f(x)=-38:
f(x)=5x+21/x
-38 = 5x + 21/x
-38x = 5x^2 + 21
0 = 5x^2 + 38x + 21

Solved by pluggable solver: SOLVE quadratic equation with variable

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=1024 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: -0.6, -7. Here's your graph:

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