[Toán 9] Đề học sinh giỏi lớp 9 ngày 1-3-2009

L

luckystudent97

sửa lại đề đi jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj
 
N

nhimcoi6

Cho đa thức f(x)=mx^3+(m-2)x^2 -(3n-3x) - 4m
Xác định m,n sao cho đa thức f(x) chia hết x+1 và x-3
giải: đa thức f(x) chia hết cho x+1 nên f(-1)=0 =>m.(-1)^3+(m-2).(-1)^2-(3n-3.(-1))-4m =0 =>-m+m-2-3n-3-4m =0
=> 3n+4m=-5 (1)
đa thức f(x) chia hết cho x-3 nên f(3)=0 =>m.3^3+(m-2).3^2-(3n-3.3)-4m =0 =>27m+9m-18-3n+9-4m =0
=>3n-32m=-9 (2)
từ (1) và (2) suy ra m=0,5 ; n=6,5:4=1,625
 
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