Answer:
C. √2/2
Explanation:
A 45 degree angle occurs in a 45 - 45 - 90 right triangle. In this special triangle, the side lengths are always 1 - 1 - √2. Always opposite the 45 degree angles is 1. And opposite the largest angle 90 is the largest side √2.
The sine function is the ratio opposite over tangent. The sin of 45 is then 1/√2 which simplifies to √2/2.