Znajdz wszystkie wartosci rzeczywiste parametru m,
dla ktorego rownanie ma 3 rozne pierwiastki rzeczywiste x^2+(m-2)x=3|x|-1
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Odp. m=1 lub m=3
x² + (m-2)x = 3IxI -1
Z def. wartości bezwzględnej:
IxI = x, dla x ≥ 0
= - x, dla x < 0
dla x ≥ 0
(1)
x²+(m-2)x = 3x-1
x²+(m-2)x-3x+1 = 0
x²+mx-2x-3x+1 = 0
x²+mx-5x+1 = 0
x²+(m-5)x+1 = 0
dla x < 0
(2)
x²+(m-2)x = -3x-1
x²+(m-2)x+3x+1 = 0
x²+mx-2x+3x+1 = 0
x²+mx+x+1 = 0
x²+(m+1)x+1 = 0
Rozpatrujemy dwa przypadki:
1.
Δ1 > 0 i Δ2 = 0
lub
2.
Δ1 = 0 i Δ2 > 0
1.
x²+(m+1)x+1 = 0
Δ = (m+1)²-4 = 0
(m+1)²-4 = 0
m²+2m+1-4 = 0
m²+2m-3 = 0
Δm = 4+12 = 16
√Δm = 4
m1 = (-2+4)/2 = 1
m2 = (-2-4)/2 = -3 ∉ D
dla m = 1
x > 0
dla m = -3
x = -1 < 0 ∉ D
m = 1
-------
2.
x²+(m-5)x+1 = 0
Δ = (m-5)²-4 = 0
m²-10m+25-4 = 0
m²-10m+21 = 0
Δm = 100-84 = 16
√Δm = 4
m1 = (10+4)/2 = 7 ∉ D
m1 = (10-4)/2 = 3
dla m = 7
x = 1 > 0 ∉ D
Odp. m = 1 v m = 3