`4)` Cho `C=(sqrtx^4-sqrtx)/(x+sqrtx+1)+(sqrtx^4+sqrtx)/(x-sqrtx+1)`
Rút gọn `C` và tính `D=1-\sqrt{2C-4sqrtx+1}(0<=x<=1/4)`
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Điều kiện xác định:`x>=0`
`C=(sqrtx(sqrtx^3-1))/(x+sqrtx+1)+(sqrtx(sqrtx^3+1))/(x-sqrtx+1)`
`C=(sqrtx(sqrtx-1)(x+sqrtx+1))/(x+sqrtx+1)+(sqrtx(sqrtx+1)(x-sqrtx+1))/(x-sqrtx+1)`
`C=sqrtx(sqrtx-1)+sqrtx(sqrtx+1)`
`C=sqrtx(sqrtx-1+sqrtx+1)=2x`
`=>D=\sqrt{4x-4sqrtx+1}=sqrt{(2sqrtx-1)^2}`
`=>D=|2sqrtx-1|=1-2sqrtx(0<=x<=1/4)`
