cos(x) is a transcendental function, there isn't much point to scratching your head trying to solve a transcendental equation; it isn't likely to be expressible in terms of radicals anyway.
cos(x)=0,3 is also transcendental equation (I think), even so I can get approximate solution with my calculator (1,266 ...). Is there any possibility how to get approximate solution of x+cos(x)=0 with common calculator (for example the calculator in windows)?
Start by making a guess between 1 and 0, call this [itex] x_1 [/itex] calculate [itex] x_2 [/itex] ,simply repeat the process until the number stops changing. It is not incredibly fast, 20 iterations gets you around 3 digits. Keep iterating until you are tired of pushing buttons, observe the digits that do not change. The unchanging digits are your answer. If you want more digits iterate some more.