Apply the Law of Cosines to a right triangle and use a calculator to find cos(90^(∘)).
See solution.
Practice makes perfect
The Law of Cosines gives us a relation between the lengths of the sides of a triangle to the cosine of one of its angles.
Particularly, let's consider a right triangle.
We have that m∠ C = 90^(∘), and by using a calculator we get that cos(90^(∘))=0. Substituting this into the equation written above, we will get the Pythagorean Theorem.
c^2 = a^2 + b^2 - 2 a bcos(90^(∘))
⇓
c^2 = a^2 + b^2
This is why the Pythagorean Theorem is a specific case of the Law of Cosines.
