rozwiąż nierówność:
-2xkwadrat+8x+7<lub równe 0
-2x² + 8x + 7 ≤ 0 / :(-1)
2x² - 8x - 7 ≥ 0
Δ = 8² - 4 * 2 * (-7) = 64 + 56 = 120
√Δ = √120 = 2√30
x1 = (8 - 2√30)/4 = (4 - √30)/2
x2 = (8 + 2√30)/4 = (4 + √30)/2
+++++ +++++++
---------o----------o-----------
x1 ---- x2
x ∈ (-oo; x1> u <x2; +oo)
-2x²+8x + 7 ≤ 0
przyrównuje do 0 i licze pierwiastki:
-2x²+8x + 7=0
Δ=b²-4ac=64 + 56=120
√Δ=√120=2√30
x1=(-b-√Δ)/2a = (-8-2√30)/-4 = -2(4+√30)/-4 = (4+√30)/2
x2=(-b+√Δ)/2a = (4-√30)/2
a<0 - ramiona paraboli są skierowane w dół
+ + + + + + + + +
---------------*------------------------*------------------>
- - - - x2 x1 - - - - - - -
x∈ (- ∞ , x2 ) ∨ (x1 , + ∞)
czyli:
x∈( - ∞ , (4-√30)/2 > ∨ < (4+√30)/2 , + ∞)
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-2x² + 8x + 7 ≤ 0 / :(-1)
2x² - 8x - 7 ≥ 0
Δ = 8² - 4 * 2 * (-7) = 64 + 56 = 120
√Δ = √120 = 2√30
x1 = (8 - 2√30)/4 = (4 - √30)/2
x2 = (8 + 2√30)/4 = (4 + √30)/2
+++++ +++++++
---------o----------o-----------
x1 ---- x2
x ∈ (-oo; x1> u <x2; +oo)
-2x²+8x + 7 ≤ 0
przyrównuje do 0 i licze pierwiastki:
-2x²+8x + 7=0
Δ=b²-4ac=64 + 56=120
√Δ=√120=2√30
x1=(-b-√Δ)/2a = (-8-2√30)/-4 = -2(4+√30)/-4 = (4+√30)/2
x2=(-b+√Δ)/2a = (4-√30)/2
a<0 - ramiona paraboli są skierowane w dół
+ + + + + + + + +
---------------*------------------------*------------------>
- - - - x2 x1 - - - - - - -
x∈ (- ∞ , x2 ) ∨ (x1 , + ∞)
czyli:
x∈( - ∞ , (4-√30)/2 > ∨ < (4+√30)/2 , + ∞)