Решите систему уравнения 2 ( 3x-y)-5=2x-3y 5-(x-2y)=4y=16

Question

Алгебра: Решите систему уравнения 2 ( 3x-y)-5=2x-3y 5-(x-2y)=4y=16

alinka393 · Accepted Answer

1) 4sin x*cos x = 2sin 2x = 1
sin 2x = 1/2
2x = pi/6 + 2pi*k; x1 = pi/12 + pi*k
2x = 5pi/6 + 2pi*k; x2 = 5pi/12 + pi*k

2) 4sin^2 2x - cos^2 2x = 1/2*(8sin^2 2x - 2cos^2 2x) =
= 1/2*(3sin^2 2x + 5sin^2 2x + 5cos^2 2x - 3cos^2 2x) =
= 1/2*(5(sin^2 2x + cos^2 2x) - 3(cos^2 2x - sin^2 2x) =
= 1/2*(5 - 3cos 4x) = √3/2
5 - 3cos 4x = √3
cos 4x = (5 - √3)/3
4x = +- arccos ((5 - √3)/3) + 2pi*k
x = +- 1/4*arccos ((5 - √3)/3) + pi*k/2

3) sin x*cos 2x + sin 2x*cos x = sin x*(2cos^2 x - 1) + 2sin x*cos x*cos x =
= 2sin x*cos^2 x - sin x + 2sin x*cos^2 x = sin x*(4cos^2 x - 1) =
= sin x*(2cos x - 1)(2cos x + 1) = 0
sin x = 0; x1 = pi*k
cos x = -1/2; x2 = 2pi/3 + 2pi*n; x3 = 4pi/3 + 2pi*n
cos x = 1/2; x4 = pi/3 + 2pi*m; x5 = -pi/3 + 2pi*m

MOGZ ответил