increasing and one one function

Question

If we are given a function f(x)=$x^3$$+$$3x$ for all x belong to real number .

Now as the derivative of function is always positive so the function should be increasing function and if it is always increasing function then it should be one one function also .

But when i tried , I got different result . Why ?

my try is on https://i.stack.imgur.com/J28rp.jpg

Sorry , I cannot post image as I don't have enough reputations — , Jul 19 '16 at 12:23

score 1 · Answer 1 · answered Jul 19 '16 at 12:26

1

You obtained a contradiction because you put $x_1=x_2$ into the equality AFTER you divided it by $x_1-x_2$ !

answered Jul 19 '16 at 12:26

larry01

1,816

increasing and one one function

1 Answers1