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C2 differentiation help

x values for increasing functions:
f(x) = 3/x - 4/(x^3)


I differentiated it to:

f'(x) = -3x^-2 +12x^-4

and i know you have to set it to >0 but I don't know how to solve the inequality
help :confused::frown::confused::frown::confused:
Reply 1
Start by multiplying through by x4x^4 (which is never negative, so the > sign doesn't change). You end up with a quadratic inequality to solve.

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