`C=(sqrt{a}+2)/(sqrt{a}+3)-5/(a+sqrt{a}-6)+1/(2-sqrt{a})`
`ĐKXĐ:a>=0,a ne 4`
`=(sqrt{a}+2)/(sqrt{a}+3)-5/((sqrt{a}-2)(sqrt{a}+3))-1/(sqrt{a}-2)`
`=[(sqrt{a}+2)(sqrt{a}-2)-5-(sqrt{a}+3)]/(a-sqrt{a}-6)`
`=(a-4-5-sqrt{a}-3)/(a-sqrt{a}-6)`
`=(a-sqrt{a}-12)/(a-sqrt{a}-6)`
`=(sqrt{a}-4)/(sqrt{a}-2)`
`C in Z`
`=>(sqrt{a}-4)` $\vdots$ `sqrt{a}-2`
`=>sqrt{a}-2-2` $\vdots$ `sqrt{a}-2`
`=>2` $\vdots$ `sqrt{a}-2`
`=>sqrt{a}-2 in Ư(2)={+-1,+-2}`
`=>sqrt{a} in {1,3,0,4}`
`=>a in {0,1,9,16}`
