bai 3
x^2-2(m-1)x+m+1=0
∆'=m^2-2m+1-m-1=m(m-3)
a)
m=-1;∆'=4 =>
x1=(-2-2)=-4
x2=(-2+2)=0
b)
dk co nghiem ≠0 m€(-vc;-1)U(-1;0]U[3; vc)
x1/x2+x2/x1=4
<=>(x1^2+x2^2)=4x1x2
<=>(x1+x2)^2=6x1x2
vi et
4(m-1)^2=6(m+1)
2(m^2-2m+1)=3m+3
2m^2-7m-1=0
m=(7-√57)/4(n)
m=(7+√57)/4(n)
 

bài 5

bai 4
a)
AB tiep tuyen (O,r) tai B =^ ABO=90°
D€AB=> ^OBD=90°
^DMO =90° {theo cach dung
=> ^DMO=^DBO
hai goc nay cung nhin canh DO =>tg DOMB noi tiep
=> bon diem O,B,D,M € dg tron dg kinh DO
b)
c.m tuong tu tu giac EMOC noi tiep
cac goc noi tiep (^B=^C)=>goc EDO=goc DEO
∆D0E can tai O
OM la duong cao => la trung tuyen => MD=ME