## Answer :

1.

**Sine (sin)**: The ratio of the opposite side to the hypotenuse.

[tex]\[ \sin(\theta) = \frac{\text{opposite}}{\text{hypotenuse}} \][/tex]

2.

**Cosine (cos)**: The ratio of the adjacent side to the hypotenuse.

[tex]\[ \cos(\theta) = \frac{\text{adjacent}}{\text{hypotenuse}} \][/tex]

3.

**Tangent (tan)**: The ratio of the opposite side to the adjacent side.

[tex]\[ \tan(\theta) = \frac{\text{opposite}}{\text{adjacent}} \][/tex]

Next, we look at the reciprocal functions:

1.

**Cosecant (csc)**: The reciprocal of sine.

[tex]\[ \csc(\theta) = \frac{1}{\sin(\theta)} = \frac{\text{hypotenuse}}{\text{opposite}} \][/tex]

2.

**Secant (sec)**: The reciprocal of cosine.

[tex]\[ \sec(\theta) = \frac{1}{\cos(\theta)} = \frac{\text{hypotenuse}}{\text{adjacent}} \][/tex]

3.

**Cotangent (cot)**: The reciprocal of tangent.

[tex]\[ \cot(\theta) = \frac{1}{\tan(\theta)} = \frac{\text{adjacent}}{\text{opposite}} \][/tex]

Given these definitions, the reciprocal ratio that represents the adjacent side over the opposite side is

**cotangent**.

Thus, the correct answer is:

O cotangent