21. x^2-14x+24=0
x=7+-sqrt(49-24)=7+-5 x1=2 x2=12
x^2+5x-66=0 x=[-5+-sqrt(25+264)]/2=[-5+-17]/2
x1=-11 x2=6
-x^2+17x+45=0
x=[-17+-sqrt(289+180)]/-2=[-17+-sqrt(469)]/2
-x^-20x-91=0
x=10+-sqrt(100-91)=10+-3
x1=13 x2=7
22.
2x^2+3x+1=0
x=[-3+-sqrt(9-8)]/4=[-3+-1]/4
x1=-1 x2=-1/2
3x^2+5x-2=0
x=1/6(-5+-sqrt(25+24))=1/6(-5+-7)
x1=-2 x2=1/3
5x^2-8x+3=0
x=1/5(4+-1) x1=1 x2=3/5
14x^2-5x-1=0
x=1/28(5+-sqrt(25+56))=1/28(5+-9)
x1=1/2 x2=-1/7