In a triangle, one angle measures x where sine of x is equal to four over five. What is the cosine of 90 minus x? Okay? The way you answer this is actually very straightforward. But you need to remember what the complimentary angle relationship for sine and cosine is. So that relationship is the sine of x is equal to the cosine of 90 minus x.

That is just a relationship you should know. Okay, and once you know this relationship, well, cosine of 90 minus x is equal to four over five. And believe it or not, that is your answer. It's super straightforward, but you need to know what that relationship is.