✔ 最佳答案
40 = 20 sin(x) + 40 cos(x) sin60
Divide both sides by 80 :
1 = (1/2) sin(x) + cos(x) sin60°
Thus, (1/2) sin(x) + cos(x) sin60° = 1
cos60° = 1/2, the equation becomes :
cos(60°) sin(x) + cos(x) sin(60°) = 1
Apply the identity sinA cosB + cosB sinA = sin(A + B) :
sin(60° + x) = 1
In the range of 0° ≤ x ≤ 360°, only sin(90°) = 1 :
sin(60° + x) = sin(90°)
60° + x = 90°
x = 30°