C

c. 1942

Xê C

C

C

C

C

a: x:(-9)=-54

=>\(x=\left(-54\right)\cdot\left(-9\right)\)

=>\(x=54\cdot9=486\)

b: \(x:\left(-12\right)=18\)

=>\(x=18\cdot\left(-12\right)=-216\)

c: \(x:\left(-5\right)=-19\)

=>\(x:5=19\)

=>\(x=19\cdot5=95\)

d: \(\left(x-28\right):\left(-12\right)=-5\)

=>\(x-28=\left(-12\right)\cdot\left(-5\right)=60\)

=>x=60+28=88

e: \(\left(x+15\right):\left(-28\right)=8\)

=>x+15=-28*8=-224

=>x=-224-15=-239

f: (x+30):(-45)=-4

=>\(x+30=\left(-45\right)\cdot\left(-4\right)=180\)

=>x=180-30

=>x=150

a) x : (-9) = -54

x= -54 . (-9)= 486

________

b) x : (-12) = 18

x= 18. (-12)= -216

_________

c) x : (-5) = -19

x= (-19). (-5)= 95

__________

d) (x - 28) : (-12) = -5

(x-28)= (-5). (-12)= 60

x= 60+28= 88

_______

e) (x + 15) : (-28) = 8

(x+15)= 8. (-28)= -224

x= -224 - 15 = - 239

__________

f) (x + 30) : (-45) = -4

(x+30)= -4. (-45)= 180

x= 180 - 30=150

B

B

Chọn B

Ta có : \(P=3\sqrt{6}\sqrt{\frac{a^2}{a^2-b^2-c^2}+\frac{b^2}{b^2-c^2-a^2}+\frac{c^2}{c^2-a^2-b^2}}\)   = \(3\sqrt{6}.Q\)

Thấy : \(a^2-b^2-c^2=\left(b+c\right)^2-b^2-c^2=2bc\) ( do a + b + c = 0 )

Suy ra : \(\frac{a^2}{a^2-b^2-c^2}=\frac{a^2}{2bc}\) . CMTT : \(\frac{b^2}{b^2-c^2-a^2}=\frac{b^2}{2ac};\frac{c^2}{c^2-a^2-b^2}=\frac{c^2}{2ab}\) 

Suy ra : \(Q=\sqrt{\frac{a^2}{2bc}+\frac{b^2}{2ac}+\frac{c^2}{2ab}}=\sqrt{\frac{a^3+b^3+c^3}{2abc}}=\sqrt{\frac{3abc}{2abc}}=\sqrt{\frac{3}{2}}\)  ( vì a + b + c = 0 )

Khi đó : \(P=3\sqrt{6}.\sqrt{\frac{3}{2}}=9\) là 1 số nguyên 

( Q.E.D) 

63

C

c

D

D

D