a)
2x^3 + 300 = 50 |-300
2x^3=-250 |:2
x^3=-125
\sqrt[3]{x^3} = \sqrt[3]{-125}
x=-5
b)
(4x^2-8x)(x^2-16)=0
4x(x-2)(x-4)(x+4)=0
4x=0 \vee\ x-2=0 \vee\ x-4=0 \vee\ x+4=0
x=0 \vee x=2 \vee\ x=4 \vee\ x=-4
c)
12x^4+5x^3-2x^2=0
x^2(12x^2+5x-2)=0
x^2=0 => x=0
lub
12x^2+5x-2=0
\Delta=b^2-4ac=5^2-4*12*(-2)=25+96=121
\sqrt\Delta=11
x_1=\frac{-b-\sqrt\Delta}{2a}=\frac{-5-11}{2*12}=\frac{-16}{24}=-\frac{2}{3}
x_2=\frac{-b+\sqrt\Delta}{2a}=\frac{-5+11}{2*12}=\frac{6}{24}=\frac{1}{4}
x=0\vee\ x=-\frac{2}{3} \vee x=\frac{1}{4}