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A triangular piece of wood has side lengths 14 cm, 19 cm and 20 cm. The angle between the 14 cm and
19 cm sides need to be known to see if it will fit properly into a cabinet.
What is the angle, accurate to onedecimal place, between the 14 cm and 19 cm sides?
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Use the cosine law
20^2 = 14^2 + 19^2 - 2*14*19*cos(a).
where "a" is the sough angle between the 14 cm and 19 cm sides. It gives
cos(a) = = 0.295113.
Hence, a = arccos(0.295113) = 1.271 radians = 72.8 degrees (rounded as requested).
Solved.