1) 20x²+x-1=0
2) 8x²+10x+3=0
3)-6x²+7-2=0

20x²+x-1=0
д=b^2-4ac=1^2-4*20*(-1)=81 = 9^2
x1=(-1-9)\40=-1\4  x2=(-1+9)\40=1\5
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8x²+10x+3=0
д=4=2^2
x1,2=(-10+-2)\16=-1\2; -3\4
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-6x²+7-2=0 
-6x^2=-7+2
-6x^2=-5
6x^2=5
x^2=5\6
x1=[tex] -\sqrt{ \frac{5}{6} } [/tex]  [tex] x2=\sqrt{ \frac{5}{6} } [/tex]