i think this way is easear
sqrt{X+\sqrt{X+\sqrt{X+...}}}=5
sqrt{5x4+\sqrt{5x4+\sqrt{5x4+...}}}=5 if it is + you will bring 5 if it is - you will bring 4
let s say:
sqrt{12+\sqrt{12+\sqrt{12+...}}}=x
we can write it like
sqrt{4x3+\sqrt{4x3+\sqrt{4x3+...}}}=x so x will be 4 because + we choosing bigger one