calculus
posted by Alex .
Determine where the given function is concave up or where it is concave down:
f(x)=9x/x^2+49

f = 9x/(x^2 + 49)
f is concave up where f'' > 0
f' = 9(x^2  49) / (x^2 + 49)^2
f'' = 18x(x^2  147)/(x^2 + 49)^3
f'' < 0 where 0 < x < √147 or x < √147
f'' > 0 where √147 < x < 0 or x > √147