and i cant use anything but thisdefinition to solve it

we need to prove that for every N>0 there is M>0 so for every x>M

we have f(x)>N .

i have a solution of a similar question:

the solution is:

we take we find M that fits it.

we clame that M=

if x>M then x>

so

i cant use the similar question because i cantisolate x on one side.