5.
[tex]\it a)\ \ \underbrace{x^2}_ {\geq0}=\ \underbrace{-4}_{ < 0} \Rightarrow S=\O\\ \\ \\ b)\ \ -x^2=25\Big|_{\cdot(-1)} \Rightarrow x^2=-25 \Rightarrow S=\O\\ \\ \\ d)\ 2x^2-16=16 \Big|_{+16} \Rightarrow 2x^2=32 \Big|_{:2} \Rightarrow x^2=16 \Rightarrow \sqrt{x^2}=\sqrt{16} \Rightarrow \\ \\ \\ \Rightarrow |x|=4 \Rightarrow x=\pm4 \Rightarrow S=\{-4,\ 4\}[/tex]
6.
[tex]\it a)\ \ x^2=\dfrac{25}{16} \Rightarrow \sqrt{x^2}=\sqrt{\dfrac{25}{16}} \Rightarrow |x|=\dfrac{5}{4} \Rightarrow x=\pm\dfrac{5}{4}\\ \\ \\ b) \ \ x^2=\dfrac{169}{196} \Rightarrow \sqrt{x^2}=\sqrt{\dfrac{169}{196}} \Rightarrow |x|=\dfrac{13}{14} \Rightarrow x=\pm\dfrac{13}{14}[/tex]
[tex]\it d)\ \ 2x^2=\dfrac{72}{25}\ \Big|_{\cdot\frac{1}{2}} \Rightarrow x^2=\dfrac{36}{25} \Rightarrow \sqrt{x^2}=\sqrt{\dfrac{36}{25}} \Rightarrow |x|=\dfrac{6}{5} \Rightarrow x=\pm\dfrac{6}{5}[/tex]
