1)

x-3=0

x=3

2)

[tex] \sqrt[3]{2x - 1} = - 3 \\ 2x - 1 = ( - 3) {}^{3} \\ 2x = - 27 + 1 \\ 2x = - 26 \\ x = - 26 \div 2 \\ x = - 13[/tex]

3)

[tex]( \frac{1}{2} ) {}^{x} \geqslant \frac{1}{16} \\ 2 {}^{ - x} \geqslant {2}^{ - 4} \\ - x \geqslant - 4 \\ x \leqslant 4 \\ x \: \epsilon \: ( - \infty ; \: 4][/tex]