Question

Triangle M N L is shown. Angle M N L is a right angle. The length of N L is 15 and the length of hypotenuse M L is 25.
Given right triangle MNL, what is the value of cos(M)?

Three-fifths
Three-fourths
Four-fifths
Five-thirds

Answer 1

Since ∠N is 90°, ML is the hypotenuse. Use Pythagoras: MN^2 + NL^2 = ML^2 ⇒ MN^2 + 15^2 = 25^2 ⇒ MN = 20.
cos(M) = adjacent/hypotenuse = MN/ML = 20/25 = 4/5.
Answer: Four-fifths.