In the triangle ABC, ∠ a = 30 °, AC = 40, BC = 25, find AB (important process) I know the formula, but I don't know the operation of sin, Tan, con and so on. Do me a favor,

Cosine theorem
AB^2+AC^2-2AB*AC*cosA=BC^2
Cosa = half root 3
Solution
AB = 20 3 + - 15

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