`2(x^2+18)=7\sqrt(x^3+27)(x>=-3)`

`->4(x^2+18)^2=49(x^3+27)`

`->4x^4+144x^2+1296=49x^3+1323`

`->4x^4-49x^3+144x^2-27=0`

`->(x^2-7x-3)(4x^2-21x+9)=0`

`->x^2-7x-3=0` hoặc `4x^2-21x+9=0`

`->x^2-7x+49/4=61/4` hoặc `x^2-21/4x+441/64=297/64`

`->(x-7/2)^2=61/4` hoặc `(x-21/8)^2=297/64`

`->x-7/2=(+-\sqrt61)/2` hoặc `x-21/8=(+-3\sqrt33)/8`

`->x=(7+-\sqrt61)/2(tm)` hoặc `x=(21+-3\sqrt33)/8(tm)`

`->S={(7+-\sqrt61)/2;(21+-3\sqrt33)/8}`