Đáp án:
`C=sqrt5+1`
Giải thích các bước giải:
`C=sqrt{4+sqrt{10+2sqrt5}}+sqrt{4-sqrt{10+2sqrt5}}`
Vì `sqrt{4+sqrt{10+2sqrt5}}>0`
`sqrt{4-sqrt{10+2sqrt5}}>0`
`=>C>0`
`C^2=4+sqrt{10+2sqrt5}+4-sqrt{10+2sqrt5}+2sqrt{16-(10+2sqrt5)}`
`C^2=8+2sqrt{6-2sqrt5}`
`C^2=8+2sqrt{5-2sqrt5+1}`
`C^2=8+2sqrt{(sqrt5-1)^2}`
`C^2=8+2(sqrt5-1)`
`C^2=6+2sqrt5=5+2sqrt5+1=(sqrt5+1)^2`
`=>C=sqrt5+1`(do `C>0`)
