Question

Express cos A as a fraction in simplest terms.

Answer 1

See below

Explanation:

Here is one way

cos^2 + sin^2 = 1

cos^2 = 1 - sin^2

For angle A cos^2 = 1 - (10/26)^2

cos ^2 = 1 - 100/676

= 576/676

cos A = 24/26 = 12/13

Another way would be to use the Pythagorean theorem to find length of AB .... then cos A = length AB / 26