f(x)=√([x]−1)+√(4−[x])
For f(x) to be defined,
[x]−1≥0 and 4−[x]≥0
⇒1≤[x]≤4
⇒1≤x<5
For,
1) x∈[1,2)
[x]=1
⇒√([x]−1)+√(4−[x])=√3
2) x∈[2,3)
[x]=2
⇒√([x]−1)+√(4−[x])=1+√2
3) x∈[3,4)
[x]=3
⇒√([x]−1)+√(4−[x])=1+√2
4) x∈[4,5)
[x]=4
⇒√([x]−1)+√(4−[x])=√3
Thus, the range of the function is {√3,1+√2}