Prove that cos² x + cos² (x + π/3) + cos² (x – π/3) = 3/2.

Question

TextDouble Angle Formulae for Trigonometric Functions

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tan 4x = 4tan x (1 – tan² x) / (1 – 6tan² x + tan⁴ x)

cos 4x = 1 – 8sin² x cos² x

Find the value of tan π/8.

TextDouble Angle Formulae for Trigonometric Functions

If tan x = 3/4, π < x < 3π/2, find the value of sin x/2, cos x/2 and tan x/2.

tan x = – 4/3, x in quadrant II

cos x = – 1/3, x in quadrant III