a]
[tex]x^2-25=0\\\\(x+5)(x-5)=0\\\\x=-5 \ \vee \ x=5[/tex]
b]
[tex]x^2-8=0\\\\(x+\sqrt8)(x-\sqrt8)=0\\\\(x+2\sqrt2)(x-2\sqrt2)=0\\\\x=-2\sqrt2 \ \vee \ x=2\sqrt2[/tex]
c]
[tex]2x^2-4=0 \ \ |:2\\\\x^2-2=0\\\\(x+\sqrt2)(x-\sqrt2)=0\\\\x=-\sqrt2 \ \vee \ x=\sqrt2[/tex]
d]
[tex]x^2+5x-6=0\\\\a=1, \ b=5, \ c=-6\\\\\Delta=5^2-4\cdot1\cdot(-6)=25+24=49\\\\\sqrt{\Delta}=\sqrt{49}=7\\\\x_1=\frac{-5-7}{2}=-6\\\\x_2=\frac{-5+7}{2}=1[/tex]
e]
[tex]x^2-7x-8=0\\\\a=1, \ b=-7, \ c=-8\\\\\Delta=(-7)^2-4\cdot1\cdot(-8)=49+32=81\\\\\sqrt{\Delta}=\sqrt{81}=9\\\\x_1=\frac{-(-7)-9}{2}=-1\\\\x_2=\frac{-(-7)+9}{2}=8[/tex]
