Hi!

I got a pretty hard problem to solve:

$\displaystyle $${7^x} + {4^x} = {25^x}$$$

I simplified it with $\displaystyle $${25^x}$$$ and I got:

$\displaystyle $${{{7^x}} \over {{{25}^x}}} + {{{4^x}} \over {{{25}^x}}} = 1$$$

from now on, in my textbook is written to use the monotony of the exponential function in order to solve this, the problem is that I don't really understand what they mean and I would really appreciate if you explain me!