1) wyznacz współczynniki wielomianu W(x)=2x³+ax²+b
jeśli w(1)=5 w(2)=2
2) Zapisz w postaci iloczynowej a następnie wyznacz pierwiastki wielomianu
w(x)=(2x+7)(2x³-5x-3)
w(x)=x³-7x²-3x+21
w(x)=x³-5x²+4x
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1.
W(x) = 2x³ + ax² + b
W(1) = 2 * 1³ + a * 1² + b = 2 + a + b
W(2) = 2 * 2³ + a * 2² + b = 16 + 4a + b
W(1) = 5
W(2) = 2
2 + a + b = 5
16 + 4a + b = 2
a + b = 3
4a + b = -14 /*(-1)
a + b = 3
-4a - b = 14
---------------------
-3a = 17
a = -17/3
a + b = 3
-17/3 + b = 3
b = 9/3 - (-17/3)
b = 26/3
odp. a = -17/3 b = 26/3
2.
w(x)=(2x+7)(2x³-5x-3)
w(x) = (2x + 7)(2x³ - 2x - 3x - 3)
w(x) = (2x +7)[ 2x(x² - 1) - 3(x + 1) ]
w(x) = (2x +7)[ 2x(x - 1)(x + 1) - 3(x + 1) ]
w(x) = (2x +7)(x + 1)[ ( 2x(x - 1) - 3 ]
w(x) = (2x +7)(x + 1)( 2x² -2x - 3 )
Δ = 4 + 24 = 28
√Δ = 2√7
x1 = (2 - 2√7)/4 = (1 - √7) / 2
x2 = (2 + 2√7)/4 = (1 + √7) / 2
w(x) = 2(2x +7)(x + 1)(x - x1)(x - x2)
-7/2 -1 x1 x2
odp. Pierwiastki wielomianu są równe: -7/2, -1 , x1, x2
w(x)=x³-7x²-3x+21
w(x) = x²(x - 7) - 3(x - 7)
w(x) = (x - 7)(x² - 3)
w(x) = (x - 7)(x - √3)(x + √3)
7 √3 -√3
odp. Pierwiastki wielomianu są równe: 7, √3 , -√3
w(x)=x³-5x²+4x
w(x) = x(x² - 5x + 4)
Δ = 25 - 16 = 9
√Δ = 3
x1 = (5 - 3)/2 = 2/2 = 1
x2 = (5 + 3)/2 = 8/2 = 4
w(x) = x(x - 1)(x - 4)
0 1 4
odp. Pierwiastki wielomianu są równe: 0, 1 , 4