Please tell how to slove ques. 72 please tell me the method used to solve it

Let {x} is fraction part of x. Then [x]=x-{x} and (x)=x+1-{x}. Now substitute these in equation.(x)^2=[x]^2+2x(x+1-{x})^2=(x-{x})^2+2xNow(x+1-{x})^2-(x-{x})^2=2x,Now apply identity a^2-b^2=(a+b)×(a-b).2x+1-2{x}=2x,{x}=1/2