In triangle ABC, angle B is straight, AB = 4, BC = 3. Find the cos of the angle BAC.

To solve this task, consider this triangle. According to the condition of the assignment, it is straight, that is, it has an angle of 90o, and we also know two sides of the triangle equal to 4cm and 3cm. It was not for nothing that I wrote these data, which are already known by condition, since this triangle refers to the so-called Pythagorean triangle with sides 3, 4, 5. In our triangle, the hypotenuse is also 5 cm. Now, knowing all three sides of the triangle, we will find the cosine of the angle BAC.

cosBAC = AB / AC = 4/5 = 0.8;

Answer: cosBAC = 0.8.