Given
right triangle with side "a" = 12 and hypotenuse "c" = 15
Find
cos(∠A)
Solution
The Pythagorean theorem tells you
... b = √(c² - a²) = √(225 - 144) = √81 = 9
The definition of the cosine tells you
... cos(A) = b/c = 9/15
... cos(A) = 3/5 . . . . . . reduce the fraction
