In a triangle abc, angle C is 90 degrees ab = 20cm cb = 16cm, find cos a.

To calculate the cos of angle A, you need to consider the ratio of the sides of a right-angled triangle. In our case, the right angle is C, which means that opposite is the hypotenuse AB = 20 cm, the adjacent leg AC and the opposite CB = 16 cm.

So, cosine is the ratio of the adjacent leg to the hypotenuse. We do not know the adjacent leg for angle A, we will find it by the Pythagorean theorem, for this we have all the necessary data. Thus, the desired side is AC = 12cm.

We compose the ratio cosA = AC / AB = 12/20 = 0.6.