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a)
x^4=3x^2
x^4-3x^2=0
x^2\left(x^2-3\right)=0
x^2=0\ tai\ x^2-3=0
x=0\ tai\ x=\sqrt{3}
b)
2x^3+3x^2=1
x^2\left(2x+3\right)=1
x=-1\ tai\ x=\frac{1}{2}