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Find cos -15π/4

Answer» Cos (-15π/4)Cos (90+75)-Sin (75)-sin (45+30)-[sin45×cos30 + cos45×sin30]-[1/√2×√3/2 + 1/2×1/√2]-(√3+1/2√2)
Cos(4π-π/4)=cosπ/4=1/√2


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