59. The side lengths of △ABC shown below are 10 m, 18 m, and 21 m. Which of the following expressions represents the measure of ∠B ?

(Note: For a triangle with sides of length a, b, and c that are opposite angles ∠A, ∠B, and ∠C, respectively, c2 = a2 + b2 - 2ab cos∠C.)

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

According to the law of cosines, 212=182+102-2*18*10cosB, cosB=(21 2-182-102)/(-2*18*10), expressed as ∠B is D