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Augustzf · Answer 1 · 2022-06-08T04:15:55+0000

cos165° + sin165°
= cos165° + sin(90° - 75°)
= cos165° + cos75°
= 2cos(165° + 75°)/2 * cos(165° - 75°)/2
= 2cos120° cos45°
= 2cos(180° - 60°) * cos(180° - 135°)
= 2 * [- cos60°] * [- cos135°]
= 2 * (-1/2) * (-135°)
= cos135°

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