# Simplify the following expressions: 1. cos(180° + x) + cos(180° - x) 2. cos(126°)cos(36°) + sin(126°)sin(36°)

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The expression

cos(180° + x) + cos(180° - x)

=> -cos x - cos x

=> -2*cos x

cos(126°)cos(36°) + sin(126°)sin(36°)

=> -sin 36°*cos(36°) + cos 36°*sin(36°)

=> 0

**cos(180° + x) + cos(180° - x) = -2*cos x and cos(126°)cos(36°) + sin(126°)sin(36°) = 0**