Tìm x,y,z biết a, (y+z+1)/x=(z+x+2)/y=(x+y-3)/z=x+y+z b,x/(y+z+2)=y/(x+z+5)=z/(x+y-7)=x+y+z
Tìm x,y,z biết a, (y+z+1)/x=(z+x+2)/y=(x+y-3)/z=x+y+z b,x/(y+z+2)=y/(x+z+5)=z/(x+y-7)=x+y+z
By Valentina
By Valentina
Tìm x,y,z biết a, (y+z+1)/x=(z+x+2)/y=(x+y-3)/z=x+y+z b,x/(y+z+2)=y/(x+z+5)=z/(x+y-7)=x+y+z
Đáp án:
y+z+1x=z+x+2y=x+y−3z=1x+y+zy+z+1x=z+x+2y=x+y−3z=1x+y+z
Áp dụng t/c dãy tỉ số bằng nhau , ta có :
y+z+1x=z+x+2y=x+y−3zy+z+1x=z+x+2y=x+y−3z
= y+z+1+x+z+2+x+y−3x+y+zy+z+1+x+z+2+x+y−3x+y+z
= 2(x+y+z)x+y+z=22(x+y+z)x+y+z=2
+) 1x+y+z=2⇒x+y+z=12=0,51x+y+z=2⇒x+y+z=12=0,5
⇒⎧⎪⎨⎪⎩x+y=0,5−zx+z=0,5−yy+z=0,5−x⇒{x+y=0,5−zx+z=0,5−yy+z=0,5−x
=> 0,5−x+1x=0,5−y+2y=0,5−z−3z0,5−x+1x=0,5−y+2y=0,5−z−3z
⇒⎧⎪ ⎪ ⎪ ⎪⎨⎪ ⎪ ⎪ ⎪⎩1,5−xx=22,5−yy=2−2,5−zz=2⇒{1,5−xx=22,5−yy=2−2,5−zz=2
⇒⎧⎪⎨⎪⎩1,5−x=2x2,5−y=2y−2,5−z=2z⇒{1,5−x=2×2,5−y=2y−2,5−z=2z
⇒⎧⎪⎨⎪⎩1,5=3x2,5=3y−2,5=3z⇒{1,5=3×2,5=3y−2,5=3z
⇒⎧⎪ ⎪⎨⎪ ⎪⎩x=0,5y=56z=−56
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