Question

3cos2x+4-5cosx=0 Алгебра 10 класс

Answer 1

3Cos2x + 4 - 5Cosx = 0

3(2Cos²x - 1) + 4 - 5Cosx = 0

6Cos²x - 3 + 4 - 5Cosx = 0

6Cos²x - 5Cosx + 1 = 0

Cosx = m , - 1 ≤ m ≤ 1

6m² - 5m + 1 = 0

D = (- 5)² - 4 * 6 * 1 = 25 - 24 = 1

$m_{1} =\frac{5+1}{12}= \frac{1}{2}\\\\m_{2}= \frac{5-1}{12}= \frac{1}{3} \\\\Cosx=\frac{1}{2} \\\\x=+-arcCos\frac{1}{2}+2 \pi n\\\\x=+-\frac{\pi} {3}+2 \pi n\\\\Cosx=\frac{1}{3} \\\\x=+-arcCos\frac{1}{3}+2 \pi n$

Answer 2

на фото......................