Why is Sine used to determine the X component of vector B, and Cosine used to determine the Y component?

Normally I use google for math questions, but this seems pretty specific and I wasn't sure what to look for, and the practice problem didn't have an explanation either. I don't know why either of these operations are used when they are, instead of a different one. It wouldn't matter in this problem because of the 45 degree angle, but I would like to know for future reference. Would Tangent ever be used for a problem like this either? Thanks in advance for the answers.