Find the value of the expression

[Hint: Simplify the expression to =

If x = sec ϕ – tan ϕ and y = cosec ϕ + cot ϕ, then show that xy + x – y + 1 = 0.

[Hint: Find xy + 1 and then show tan x – y = –(xy + 1)]

If θ lies in the first quadrant and then find the value of cos(30° + θ) + cos (45° – θ) + cos (120° – θ)

Find the general solution of the equation

5cos²θ + 7sin²θ – 6 = 0

Find the general solution of the equation sin x – 3sin2x + sin3x = cos x – 3cos2x + cos3x