Answer:
8/9 (choice b)
Explanation:
The trigonometric ratios are based on the ratios of different sides.
If you remember SOH CAH TOA =
sine (sin) opposite hypotenuse
cosine (cos) adjacent hypotenuse
tangent (tan) opposite adjacent
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This is a nuemonic for these ratios.
the opposite side is the side that is directly across from the reference angle, the hypotenuse is the longest side, and the adjacent side is the side other than these two.
So cos C = adjacent side / hypotenuse side.
Since 18 is greater than 16 and 9, 18 is the hypotenuse.
the adjacent side is the side other than the opposite side and the hypotenuse which is 16
therefore cos C = 16 / 18 = 8 / 9.