1) x^2-â5*x+1/4=0
x1=(â5+2)/2, x2=(â5-2)/2
2) x^2-x=0
3) 4-4*6*a>=0
a<=1/6
x1+x2=-1/3ï¼x1*x2=a/6
|x1-x2|=2
(x1-x2)^2=4
(x1+x2)^2-4x1*x2=4
1/9-4a/6=4
a=-35/6
4) b^2-4c>=0
b^2>=4c
(b,c)=(2,1)(3,1)(3,2)(4,1)(4,2)(4,3)(4,4)(5,1)(5,2)(5,3)(5,4)(5,5)(5,6)(6,1)(6,2)(6,3)(6,4)(6,5)(6,6)
1+2+4+6+6=19
5) (1) 6x^2-3x-2=0ä¸¤æ ¹ä¸ºaï¼b
a+b=1/2ï¼ab=-1/3
x1+x2=-1/a-1/b=-(a+b)/(ab)=3/2
x1*x2=(-1/a)(-1/b)=1/(ab)=-3
æ¹ç¨ï¼x^2-3/2*x-3=0å³ 2x^2-3x-6=0
(2) 4x^2-3x-2=0ä¸¤æ ¹ä¸ºaï¼b
a+b=3/4ï¼ab=-1/2
x1+x2=a^2+b^2=(a+b)^2-2ab=9/16+1=25/16
x1*x2=a^2*b^2=(ab)^2=1/4
æ¹ç¨ï¼x^2-25/16*x+1/4=0å³ 16x^2-25x+4=0
6) x1+x2=(2m-1)/mï¼x1*x2=(m-2)/m
(x1-3)(x2-3)=5m
x1*x2-3(x1+x2)+9=5m
(m-2)/m-3(2m-1)/m+9=5m
(m-2)-3(2m-1)+9m=5m^2
5m^2-4m-1=0
(m-1)(5m+1)=0
m=1æm=-1/5(èå»)
7) 4(m+1)^2-4(4m+1)>=0 (1)
2(m+1)<0 (2)
4m+1<0 (3)
è§£å¾ m<-1
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