## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

For a right triangle with legs $a$, $b$ and the hypotenuse $c$, the Pythagorean theorem states that: $$c^2=a^2+b^2.$$ We plug in the side lengths to check if the triangle is right: $$\sqrt{4^2+5^2}=\sqrt{41}\ne6 .$$ This statement is false, so the triangle is not right.