How do i know when to use inverse law of cosine instead of law of cosine or are they the same?

Step-by-step explanation:

There is no such thing as the inverse Law of Cosines. You CAN use the law to find a missing angle, which is found by finding the inverse cos of a ratio. For example, if you have all 3 sides of a non-right triangle and you are looking for the measure of an angle, you would do all the required math, and in the end you would have that cos (x) = some fraction. Take the inverse cos on your calculator of this fraction and get the angle value.

In other words, the Law of cosines can be used to find both a missing side OR a missing angle.