SOLUTION: HI, how do I solve: For the given rational function f, find all values of x for which f(x) has the indicated value. f(x) = 5x + 21/x ; f(x) = -38 thanks Paola

Algebra ->  Radicals -> SOLUTION: HI, how do I solve: For the given rational function f, find all values of x for which f(x) has the indicated value. f(x) = 5x + 21/x ; f(x) = -38 thanks Paola      Log On


   

Question 444783: HI, how do I solve:
For the given rational function f, find all values of x for which f(x) has the indicated value.

f(x) = 5x + 21/x ; f(x) = -38
thanks
Paola
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
f(x) = 5x + 21/x ; f(x) = -38
..
-38 = 5x + 21/x
multiply by x
-38x=5x^2+21
5x^2+38x+21=0
solve by quadratic formula
a=5, b=38, c=21
x=[-38+-sqrt(38^2-4*5*21)]/2*5
x=[-38+-sqrt(1024)]/10
x=(-38+-32)/10
x=-70/10=-7
or
x=-6/10=-.6