Question

page 15 of 15
The Law of Cosines Quick Check
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Use the Law of Cosines, b2=a2+c2−2ac⋅cosB
, to find the value of angle B
in a right triangle, where a=9
, b=40
, and c=41
.(1 point)

90.01 degrees

77.32 degrees

78.01 degrees

84.55 degrees

Answer 1

Use the law of cosines:
cos B = (a^2 + c^2 − b^2) / (2ac) = (9^2 + 41^2 − 40^2) / (2·9·41) = 162/738 = 9/41.

B = arccos(9/41) ≈ 77.32 degrees.