Question

What is cos A?

15
С
36
B
Enter your answer as a simplified fraction, in
the box
COS A

Answer 1

`cos A = (5)/(13)`

Explanation:

The given triangle, ∆ABC is a right triangle.

To find cos A, we'd need to apply the trigonometric ratio formula, which is cos A = adjacent length/hypotenuse length

From the ∆ given,

AC = adjacent = 15,

BC = opposite = 36

We are not given the hypotenuse length AB.

==>Find the hypotenuse length AB, using the Pythagorean theorem formula:

c² = a² + b²

AB² = 15² + 36² = 225 + 1296 = 1521

AB = √1521

AB = 39

==>Find cos A:

cos A = adjacent/hypotenuse

`cos A = (adjacent)/(hypotenuse)`

Adjacent = AC = 15

Hypotenuse = AB = 39

`cos A = (15)/(39)`

`cos A = (5)/(13)`