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You cannot do this; the information is not sufficient. You can have (say) a line of length 3 and a line of length 4 making any angle that you choose. Imagine two sticks hinged together at one end. If you know all three sides of a triangle you can use the cosine law from trigonometry: a² = b² + c² 2bc cos(α) where α is the angle between the sides of length b and c. First solve for cos(α) [which may be positive or negative] and then for α itself. The angle will be somewhere from 0 to 180 degrees. RD
 


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