The picture shows a triangular island.
which expression shows the value of c?

b over sin 45 degrees

b over cos 45 degrees

a cos 45°

a sin 45°

For a right triangle, we have he advantage of using the trigonometric functions like cosine and sine. 

If you use cosine function:
cos45 = adjacent/hypotenuse
cos 45 = b/c
c = b/cos 45

If you use sine function:
sin 45 = opposite/hypotenuse
sin 45 = a/c
c = a/sin45

From the choices, the answer is b over cos 45 degrees