7) 5cos^2 x + 3sin^2 x - 2cos 2x - 4sin 2x = 0 Довольно просто на самом деле. cos 2x = cos^2 x - sin^2 x; sin 2x = 2sin x*cos x 5cos^2 x + 3sin^2 x - 2cos^2 x + 2sin^2 x - 8sin x*cos x = 0 5sin^2 x - 8sin x*cos x + 3cos^2 x = 0 Делим все на cos^2 x, не равный 0 5tg^2 x - 8tg x + 3 = 0 Квадратное уравнение относительно тангенса (tg x - 1)(5tg x - 3) = 0 tg x = 1; x = pi/4 + pi*k tg x = 3/5; x = arctg(3/5) + pi*k ~ 31 градус + pi*k Промежутку [-pi/2; 2pi] принадлежат корни x1 = arctg(3/5), x2 = pi/4, x3 = arctg(3/5) + pi, x4 = 5pi/4
4x² + 1 = 0 a = 4 | b = 0 | c = 1
D = b² - 4ac = 0 - 4 * 4 * 1 = 0 - 16 = -16 < 0, корней нет
2m² - 3m = 8 -3m
2m² - 3m - 8 + 3m = 0
2m² - 8 = 0 a = 2 | b = 0 | c = -8
D = b² - 4ac = 0 - 4 * 2 * (-8) = -64 < 0, нет корней
3x² - 4x = 0 a = 3 | b = -4 | c = 0
D = b² - 4ac = 16 - 4 * 3 * 0 = 16 > 0, 2 корня
x₁ = -b + √D/2a = 4 + 4/6 = 8/6 = 4/3
x₂ = -b - √D/2a = 4 - 4/6 = 0/6 = 0
4x² - 9 = 0 a = 4 | b = 0 | c = -9
D = b² - 4ac = 0 - 4 * 4 * (-9) = 144 > 0, 2 корня
x₁ = -b + √D/2a = 0 + 12/8 = 12/8 = 3/2 = 1,5
x₂ = -b - √D/2a = 0 - 12/8 = -12/8 = -3/2 = -1,5
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