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ab=25.9, ac=14.2, and bc= 21.5. What is A

We can use the Law of Cosines to solve this.

21.5^2 = 14.2^2 + 25.9^2  - 2(25.9)(14.2)cosA

cos A  = [21.5^2  - 14.2^2 - 25.9^2] / [ -2(25.9)(14.2)]

And using the cosine inverse, we have

arccos [ 21.5^2  - 14.2^2 - 25.9^2] / [ -2(25.9)(14.2)]  = A  = about 56.105°