3x^4+18^3+27x^2=0
Factor out 3x², then subsequently factor the remaining expression.
3x²(x²+6x+9) = 0
3x²(x+3)² = 0
The roots should be clear from the above form of the equation.
3x²(x²+6x+9) = 0
3x²(x+3)² = 0
The roots should be clear from the above form of the equation.