# What is #cos[sin^(-1)(-1/2 ) + cos^(-1)(5/13) ]#?

##### 2 Answers

#### Explanation:

Now, using

By the sum angle formula that's

#### Explanation:

These questions are confusing enough with the funky inverse function notation. The real problem with questions like this is it's generally best to treat the inverse functions as multivalued, which may mean the expression has multiple values as well.

We can also look at the value of

Anyway, this is the cosine of the sum of two angles, and that means we employ the sum angle formula:

Cosine of inverse cosine and sine of inverse sine are easy. The cosine of inverse sine and sine of inverse cosine are also straightforward, but there's where the multivalued issue comes in.

There will be generally be two non-coterminal angles that share a given cosine, negations of each other, whose sines will be negations of each other. There will generally be two non-coterminal angles that share a given sine, supplementary angles, which will have cosines that are negations of each other. So both ways we up with a

Let's take

We don't really need to consider the angle. We can think about the right triangle with opposite 1 and hypotenuse 2 and come up with adjacent

Similarly,