Find the exact value by using the sum or difference identity cos(135°+120°)
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Answer:
(1-√3)√2/4
Step-by-step explanation:
cos(135°+120° )
As we know that,
cos(135° + 120°) = cos135°.cos120° - sin135°.sin120°
= cos(90°+45°).cos(180°-60°) - sin(90°+45°).sin(180° - 60°)
= -sin45°.-cos60° - cos45°.sin60°
= -1/√2×1/2 - 1/√2 × √3 /2
= 1/2√2-√3/2√2
=( 1-√3)/2√2
= (1- √3/2√2)×√2/√2
= (1-√3)√2/2×2
= (1-√3)√2/4
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