In trapezoid ABCD, sin of angle A = √21 divided by 5, find the cosine of angle B.

univerkov | May 4, 2021 | education

The sum of the angles at the side of the trapezoid is 180, then CosABS = Cos (180 – BAD) = -CosBAD.

Let’s define CosBAD.

Cos2BAD = 1 – Sin2BAD = 1 – 21/25 = 4/25.

CosBAD = 2/5.

Then CosABS = – CosBAD = -2/5 = -0.4.

Answer: The cosine of angle B is equal to – 0.4.

One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.