Question

Find cos B exactly if a = 15, b = 11, and angle Cis a right angle

Answer 1

Final answer is
`\cos\left(B\right)=(15)/(√(346))` which is the last choice.

Explanation:

In triangle ABC, we have been given a = 15, b = 11, and angle C is a right angle.

Now using those values, we need to find the exact value of cos B.

Apply Pythagorean formula:

`AB^2=AC^2+BC^2`

`AB^2=11^2+15^2`

`AB^2=121+225`

`AB^2=346`

`AB=√(346)`

Now apply formula of cos

`\cos\left(B\right)=(BC)/(AB)`

`\cos\left(B\right)=(15)/(√(346))`

Hence final answer is
`\cos\left(B\right)=(15)/(√(346))`