Answer:
cos A = [tex]\frac{5}{13}[/tex]
Step-by-step explanation:
cos A = [tex]\frac{adjacent}{hypotenuse}[/tex]
To calculate the hypotenuse AB use Pythagoras' identity
AB² = 15² + 36² = 225 + 1296 = 1521, hence
AB = [tex]\sqrt{1521}[/tex] = 39
hence cos A = [tex]\frac{15}{39}[/tex] = [tex]\frac{5}{13}[/tex] in simplest form
