law of cosines triangle problem

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Law of Cosines

x^2  = b^2  + c^2  - 2(b)(c)cos( CAB)

x^2  = 15^2 + 17^2  - 2(15)(17)cos (108°)

x^2  =  225 + 289  - 2 (255)cos(108°)

x^2  = 514 - 510cos(108°)

x = sqrt  [  514 - 510 cos(108°) ]  ≈    25.9