In triangle ABC, angle C is 90 degrees, AC = 5, cosA = 0.8.

Given:

ABC – right triangle;

Angle C = 90 degrees;

AC = 5;

cos A = 0.8;

Find AB.

Solution:

In order to find the hypotenuse AB of the triangle ABC, we use the formula:

cos A = AC / AB.

Hence, AB = AC / cos a;

Substitute the known values into the formula and find the hypotenuse AB.

AB = 5 / 0.5 = 5 / (8/10) = 5 / (4/5) = 5/1 * 5/4 = 25/4 = 6.25;

Answer: AB = 6.25.