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Answer:
cos(20°)
Step-by-step explanation:
The angle difference formula for cosine is ...
cos(α -β) = cos(α)cos(β) +sin(α)sin(β)
If we let α = 50° and β = 30° then this matches the given expression:
cos(50° -30°) = cos(50°)cos(30°) +sin(50°)sin(30°) = cos(20°)
