a ) - 24

B ) - 65

mink tim ca tieng moi za

a/27-(5-/x/)=31

=> 27-5+/x/=31

=>22+/x/=31

=>/x/=31-22=9

=>x=9 hoac x=-9

b/(-13)-6+/x+1/=24

=>/x+1/=24+6-(-13)

=>/x+1/=30+13

=>/x+1/=43

=>x+1=43 hoac x+1=-43

=>x=42 hoac x=-44

Ta co : √a/√(b+c)=a/√a.(b+c)=2a/2√a.(b+c)≥2a/(a+b+c)

Vi a,b,c>0 nen √a/√(b+c)>2a/(a+b+c)

Tuong tu √b/√(b+c)>2b(a+b+c)

√c/√(a+b)>2c/(a+b+c)

=> VT>2a/(a+b+c) + 2b/(a+b+c) + 2c/(a+b+c)=2.(a+b+c)/(a+b+c)=2

de phai la x.(x-1)(x+4)(x+5)=84 moi dung

pt<=>[x.(x+4)].[(x-1)(x+5)]=84

<=>(x²+4x)(x²+4x-5)=84

Dat x^2+4x=a ta dc : a.(a-5)=84

=> a²-5a-84=0

=> a²+7a-12a-84=0

=>a(a+7)-12(a+7)=0

=>(a-12)(a+7)=0

=> a=12 hoac a=-7

Voi a=12 thi x²+4x=12

=>x²+4x-12=0

=>(x-2)(x+6)=0

=> a=2 hoac a=-6

Voi a=-7 thi x²+4x=-7

=>x²+4x+7=0

=>(x²+4x+4)+3=0

=>(x+2)²+3≥3>0

=> pt vo nghiem

Neu thay dung thi cho minh 1 tick nhe

cach lam , dung mk cho 3 ****

y²-2000y+1999y-1999.2000

=y.(y-2000)+1999.(y-2000)

=(y+1999)(y-2000)

1/a+[(a-3)-(a+3+a-2)=a+(a-3-a-a-+2-3)=a+a-3+2-3-a-a-=-4

2/(a+a+3)-(a+2-a+2)=2a+3-4=2a-1

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