[tex]a)\;-25+100x^2=0\Longrightarrow-1+4x^2=0\Longrightarrow4x^2=1\Longrightarrow x^2=\dfrac{1}{4}\\\Longrightarrow x=\pm\sqrt{\dfrac{1}{4}}\Longrightarrow x=\pm\dfrac{1}{2}\\\\
b)\;2x^2-98=0\Longrightarrow x^2-49=0\Longrightarrow x^2=49\Longrightarrow x=\pm\sqrt{49}\Longrightarrow x=\pm7\\\\
c)\;2x^2+5x=0\Longrightarrow x(2x+5)=0\Longrightarrow \left \{ {{x_{1}=0} \atop {2x-5=0\rightarrow x_{2}=\frac{5}{2}}} \right. \\\\
d)\;6x^2=0\Longrightarrow x^2=0\Longrightarrow x=\pm\sqrt{0}\Longrightarrow x_{1}=x_{2}=0[/tex]
