Toán Lớp 9: 1) 6x+1/4x-3
2) x-2/x^2-5
TÌM X NGUYÊN ĐỂ A NGUYÊN
MÌNH CẦN GẤP Ạ . MÌNH CẢM ƠN
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Toán Lớp 9: 1) 6x+1/4x-3
2) x-2/x^2-5
TÌM X NGUYÊN ĐỂ A NGUYÊN
MÌNH CẦN GẤP Ạ . MÌNH CẢM ƠN
Comments ( 1 )
Để A in Z
->(6x+1)/(4x-3) in Z
->6x+1 vdots 4x-3
->2(6x+1) vdots 4x-3
<=>12x+2 vdots 4x-3
<=>12x-9+11 vdots 4x-3
<=>3(4x-3)+11 vdots 4x-3
<=>11 vdots 4x-3
<=>4x-3 in Ư(11)
Ư(11)={+-1; +-11}
->4x-3 in {{+-1; +-11}
+)4x-3=1->4x=4->x=1 (Tm)
+)4x-3=-1->4x=2->x=1/2 (Ktm)
+)4x-3=11->4x=14->x=7/2 (Ktm)
+)4x-3=-11->4x=-8->x=-2 (Tm)
Vậy : x in {-2; 1} thì A=(6x+1)/(4x-3)
2)B=(x-2)/(x^2-5)
Để B in Z
->(x-2)/(x^2-5) in Z
->x-2 vdots x^2-5
->(x-2)(x+2) vdots x^2-5
<=>x^2-4 vdots x^2-5
<=>x^2-5+1 vdots x^2-5
<=>1 vdots x^2-5
<=>x^2-5 in Ư(1)
Ư(1)={+-1}
+)x^2-5=1->x^2=6->x=+-\sqrt{6} (Ktm)
+)x^2-5=-1->x^2=4->x=+-2 (Tm)
Vậy : x=+-2 thì B=(x-2)/(x^2-5) in Z