Practicing Success
Solve: $[x]^2 = x + 2\{x\}$, where [.] and {.} denote the greatest integer and the fractional part functions, respectively. |
$\{x\}=\frac{2}{3},0,0,\frac{2}{3}$ $x=-\frac{1}{3},0,1,\frac{8}{3}$ $\{x\}=-\frac{2}{3},0,0,\frac{2}{3}$ $x=\frac{1}{3},0,1,\frac{8}{3}$ $\{x\}=-\frac{2}{3},0,0,\frac{2}{3}$ $x=-\frac{1}{3},0,1,-\frac{8}{3}$ $\{x\}=-\frac{2}{3},0,1,\frac{2}{3}$ $x=\frac{1}{3},1,1,-\frac{8}{3}$ |
$\{x\}=\frac{2}{3},0,0,\frac{2}{3}$ $x=-\frac{1}{3},0,1,\frac{8}{3}$ |
$[x]^2 = x + 2\{x\}⇒[x]^2 = [x] + 3\{x\}$ so $\{x\} = \frac{[x]^2 -[x]}{3}$ so $0≤\frac{[x]^2 -[x]}{3}<1$ so $[x]^2 -[x]>0$ $[x]^2 -[x]<3$ so $[x]([x]-1)>0$ $[x]∈(-∞,0)∪[1,∞)$ $[x]^2 -[x]-3=0⇒[x]=\frac{1±\sqrt{13}}{2}$ so for $[x]^2 -[x]-3<0$ $⇒[x]∈[\frac{1-\sqrt{13}}{2},0]∪[1,\frac{1+\sqrt{13}}{2}]$ $⇒[x]=-1,0,1,2$ $\{x\}=\frac{[x]^2 -[x]}{3}⇒\{x\}=\frac{2}{3},0,0,0$ so $x=[x]^2 -2\{x\}⇒x=-\frac{1}{3},0,1,\frac{8}{3}$ |