[latex] x^{2} =15999 => x= sqrt{15999} [/latex] sau [latex]x=- sqrt{15999} [/latex]. Rezolvare: [latex] x^{2} =15999 <=> x^{2} -15999=0 <=> (x+ sqrt{15999})(x- sqrt{15999})=0. [/latex] De aici rezulta ca [latex]x+ sqrt{15999} =0[/latex] sau [latex]x- sqrt{15999}=0 [/latex], iar de aici rezulta ca x∈{[latex]- sqrt{15999} [/latex] ; [latex] sqrt{15999} [/latex]}.