Question

Find the exact value of cos A in simplest radical form.B1312СA5

Answer 1

To calculate the cosine of a determined angle of a rigth triangle without knowing the measure of the angle you have to make use of the trigonometrical ration.

`\cos \theta=(adjacent)/(hypothenuse)`

The cosine of a certain angle θ is equal to the ratio between the side sdjacent to said angle and the hypothenuse of the triangle.

For the given triangle the side adjacent to ∠A is AC=5 and the hypothenuce is AB=13

THe cosine of A is then:

`\begin{gathered} \cos A=(AC)/(AB) \\ \cos A=(5)/(13) \end{gathered}`