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2Cos²x - 5Cosx + 3 = 0
Сделаем замену :
Cosx = m , - 1 ≤ m ≤ 1
2m² - 5m + 3 = 0
D = (- 5)² - 4 * 2 * 3 = 25 - 24 = 1
(Cos(18+7))^2+(sin(18+7))^2=1;
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[]- сплошной кружок в точке х=-2
б)
х > 0
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x < 0
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х ≥0
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x ≤ 0
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