In the triangle ABC, the angle is C = 90 degrees, BC = 12 cm, AB = 15 cm. Find cosA.

The cosine of the angle cos (A) is the ratio of the adjacent AC leg to the AB hypotenuse. Find the length of the AC leg. In a triangle ABC, the angle is C = 90 degrees, which means this triangle is right-angled. According to the Pythagorean theorem in a right-angled triangle, the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the legs.
AB ^ 2 = AC ^ 2 + CB ^ 2;
15 ^ 2 = AC ^ 2 + 12 ^ 2;
AC ^ 2 = 15 ^ 2-12 ^ 2;
AC ^ 2 = 81;
AC = 9.
Hence cos (A) = 9/15 = 3/5.
Answer: cos (A) = 3/5.