Question

Which trig ratio would you use to solve for the missing angle measure? 5 A) Cos! 26 26 B Cos-1 5 C) Sin 26 Sin? 26 5​

Answer 1

Answer: Choice A)
`\cos^(-1) (5)/(26)`

You could also write
`\cos^(-1) \left((5)/(26)\right)` which is the same as writing
`\arccos\left((5)/(26)\right)`

Arccos stands for "arccosine", which is effectively the same as inverse sine. The notation
`\cos^(-1)` means inverse cosine.

We use the cosine rule because

cos(angle) = adjacent/hypotenuse.

isolating the angle leads to

angle = arccos(adjacent/hypotenuse)

We can think of arccosine as an operation to undo the cosine function. It's similar to how division is the opposite of multiplication.